CHAPTER V

RELATIVE FREQUENCY OF EARTHWORMS IN DIFFERENT REGIONS OF THE WORLD

It will be of use for various purposes to be considered later to arrive at a comprehensive view of the relative numbers of species and genera of earthworms in the four quarters of the globe. And in making this general census we shall not take into consideration the purely aquatic forms, but shall limit ourselves to the earthworms, _sensu stricto_, or Megadrili, of which, however, it is true that some members are actually lake and river dwellers. This latter fact will not, however, interfere with the usefulness of the comparative survey.

Two preliminary remarks are necessary. The opinions of naturalists vary as to the limits of genera; and a species may be a species to one and a mere variety to another. Thus it will be impossible to give a summary of the facts to be enumerated presently, which will be either absolutely accurate or which will satisfy everyone in every detail. But it is asserted that the following survey is substantially correct.

In the second place it is often possible to eliminate from the fauna of a given region those species and even genera which have been accidentally imported, a matter which will receive careful consideration on a later page. Such forms are therefore, in those cases at any rate where the evidence seems to be overwhelming, withdrawn from the list. In other cases, particularly in the Eastern region of the world, it has been found less easy to rectify the catalogues by removing what Dr Michaelsen has termed 'peregrine' forms.

We shall commence with a census of South America; the entire Continent will be divided for the present purpose into three divisions, viz. South America, Central and North America, and in the third place the West Indian Islands.

In South America we find that the bulk of the indigenous earthworms belong to the family Geoscolecidae and to a definite sub-family, viz. Geoscolecinae. These genera are _Onychochaeta_ with one species, _Hesperoscolex_ of which one species is known from the area, _Periscolex_ with one species, _Anteoides_ with two species, _Pontoscolex_ one species. _Opisthodrilus_ with two species, _Rhinodrilus_ (including either as synonyms or as sub-genera, _Thamnodrilus_, _Anteus_, _Tykonus_, _Urobenus_ and _Aptodrilus_) with no less than 49 species: _Andiodrilus_ with five species, _Holoscolex_ with one species, _Glossoscolex_ ten species, _Fimoscolex_, _Andiorrhinus_ and _Enantiodrilus_ with one species apiece.

Thus of this sub-family of Geoscolecidae we have in South America a large number of genera and a much larger number of species. Of a second sub-family of Geoscolecidae there are three species of _Criodrilus_ found in the South American Continent.

We now turn to the Megascolecidae of which a large number of species occur within the area now under consideration. The bulk of these belong to the sub-family Acanthodrilinae and they are as follows:

Of the genus _Notiodrilus_ there are ten species, of _Microscolex_ two species, of _Chilota_ 19, of _Yagansia_ 13.

A second sub-family Trigastrinae also occurs in this Continent and the following genera are permanent inhabitants, viz.:--

_Dichogaster_ (= _Benhamia_) with only three species, of which two at least are found elsewhere, and of which therefore the autochthonism is doubtful.

Finally, there is the sub-family Ocnerodrilinae comprising the following genera: _Kerria_ with ten species, _Ocnerodrilus_ (with sub-genera _Liodrilus_, _Ilyogenia_ and _Haplodrilus_) four species, which again are rather doubtful indigenes of the South American Continent.

Leaving aside certain species (of the genera _Lumbricus_, _Pheretima_, etc.) which are clearly not indigenous, the South American Continent harbours 150 kinds of earthworms which are distributed in some 19 genera. But of these a few species (_e.g._ _Onychochaeta windlei_, _Kerria macdonaldi_) stray into neighbouring regions, _i.e._ the West Indies and California. It is doubtful therefore whether they are to be referred to as limited to one of these regions and accidentally imported into the others, or whether they are genuine inhabitants of both.

The South American Continent shares with the West Indies the following genera, but the species (except in the case of _Onychochaeta windlei_, _Glossoscolex peregrinus_) are distinct; these genera are _Hesperoscolex_, _Pontoscolex_, _Dichogaster_, and _Ocnerodrilus_. _Diachaeta_ is limited to the West Indies.

The following South American genera are also found in Central and warmer North America (Mexico, California), viz. _Hesperoscolex_, _Periscolex_, _Rhinodrilus_, _Pontoscolex_, _Andiodrilus_, _Glossoscolex_, _Notiodrilus_, _Microscolex_, _Dichogaster_, _Kerria_ and _Ocnerodrilus_. But with the exception of _Hesperoscolex_, which seems to belong rather to Central America and the West Indies, _Microscolex_ and _Pontoscolex_ which are world-wide and whose original home is therefore difficult to fix, and _Dichogaster_ and _Ocnerodrilus_ which would seem rather to be rare immigrants (perhaps not truly indigenous) into South America, these genera are practically distinctively South American.

Thus we may fairly say that the genera _Anteoides_, _Opisthodrilus_, _Andiodrilus_, _Holoscolex_, _Glossoscolex_, _Rhinodrilus_, _Andiorrhinus_, _Fimoscolex_, _Enantiodrilus_, _Notiodrilus_, _Chilota_, _Yagansia_ and _Kerria_ are at least very distinctive of S. America and that they are represented by the large majority of species found in that continent, the total being 120 or slightly more.

Leaving the American Continent and adjacent islands and archipelagos, the next great land-mass to receive attention will be the Continent of Africa. In giving a census of the species and genera of earthworms which inhabit this quarter of the globe it must be premised that the facts relate only to Africa south of the Sahara. But little is known of the genera which occur in Algeria and Morocco, but from what little is known it is clear that they should come into consideration in connection with the fauna of Europe and not with that of tropical and south temperate Africa.

We have in the first place to consider an entirely peculiar family, of fair extent in genera and species, which is limited to this region of the world; that is to say with one apparent exception which is clearly only apparent. The genus _Eudrilus_ is one of the few kinds of worms that turns up in collections from every tropical part of the world and even at times from more temperate countries. It is one of those 'peregrine' forms, as Dr Michaelsen has termed them, which possess unusual facilities for extending their range. Presumably its real home is Africa. This family is known as the Eudrilidae though by some it is only regarded as a sub-family of the Megascolecidae. In this family we have the following genera: _Eudriloides_ with 11 species, _Platydrilus_ with 11 species, _Megachaetina_ with two species, _Reithrodrilus_ with one, _Stuhlmannia_ with five species, _Notykus_ and _Bogertia_ with one species each, _Metadrilus_ also with but one species, _Pareudrilus_ with perhaps five, _Libyodrilus_ with one and _Nemertodrilus_ with two species, _Metschaina_ with two species, _Eudrilus_ with two (or possibly more?) species, _Parascolex_ with four species, _Preussiella_ with two, _Buttneriodrilus_ with two, _Eminoscolex_ with 16 species, _Hyperiodrilus_, _Heliodrilus_, _Alvania_, _Rosadrilus_, _Kaffania_, _Euscolex_, _Metascolex_, _Beddardiella_, _Gardullaria_ with only one species to each genus, _Bettonia_ with three species, _Teleudrilus_ with 15 species, _Polytoreutus_ with 22 species, _Iridodrilus_ with two, _Malodrilus_ also with two, _Neumanniella_ with eight, _Eupolytoreutus_ with two and _Teleutoreutus_ with only one species.

This completes the list of the Eudrilidae. We will take the huge family Megascolecidae next; and we find in tropical Africa that the genus _Dichogaster_ alone contains at least 93 species confined to Africa, as well as a few which it shares in common with America, and the common and widely spread _D. bolavi_ which has even made its way to Europe. Of the sub-family Ocnerodrilinae we have the genus _Gordiodrilus_ with seven species, a genus which also occurs in Madagascar and the West Indies: _Nannodrilus_ with three species, _Diaphorodrilus_ with one species and a few examples of _Ocnerodrilus_ and its sub-genera, some of which are also forms that occur elsewhere in the world, for example _Nematogenia panamensis_. Of _Pygmæodrilus_ there are eight or nine species.

Of the sub-family Acanthodrilinae the Cape region of South Africa harbours some seven species of the genus _Notiodrilus_, of which one however is a West African form. The allied _Chilota_ has 13 species, and there is a peculiar genus _Holoscolex_ near to _Yagansia_ with one species. We next have to deal with the Geoscolecidae, of which a sub-family, Microchaetinae, is mainly found in Africa, the rest being found in the neighbouring Madagascar and some few in the East. _Microchaetus_ contains about 14 species, _Tritogenia_ perhaps three, _Callidrilus_ two, and the genus _Glyphidrilus_, mainly found in Asia, has one species in the region now under consideration. In addition to these Geoscolecids there is the peculiar and largely aquatic _Alma_ with six or seven species in East, West, and Central, Africa, and in the Nile region.

Summing up the genera which are found in tropical and South Africa we find that there are 44 which are abundant in, or entirely confined to, the region. In addition to these four or so occur in Africa but are either more abundant elsewhere or (as in the case of _Chilota_ and _Notiodrilus_) are equally distinctive of other parts of the world. The number of species may be estimated at 270, possibly rather more. Clearly therefore this part of the world is much richer than South America, both in numbers of genera actually found, and peculiar to the country, and numbers of species.

Passing from Africa the next definite quarter of the globe which will detain us here is the island of Madagascar, so remarkable for the Mammalian fauna which characterises it, for its lemurs, peculiar Insectivora and Carnivora, and above all by reason of the absence of the prevalent African types such as antelopes, zebras, rhinoceros etc. It is probable that a good deal still remains for discovery among the earthworms of this island; but a considerable number are already known and they are as follows:

The Eudrilidae are completely absent, a state of affairs which is paralleled by the absence of antelopes among mammals.

The sub-family Acanthodrilinae of the family Megascolecidae are represented by four species of the genus _Notiodrilus_, with which perhaps _Maheina braueri_ from the Seychelles should be included as it presents small differences from _Notiodrilus_.

Among the Megascolecinae a good many species of _Pheretima_ have been collected both on Madagascar and on certain adjacent islands; but these, with one possible exception, are forms which occur elsewhere and are often indeed very widely distributed 'peregrines,' so that it is hardly permissible to place them among the real inhabitants of Madagascar. The same arguments hold in the case of _Lampito mauritii_ and the ubiquitous _Eudrilus_ and _Pontoscolex_. But there is the peculiar _Howascolex_.

Among the Ocnerodrilinae a distinct species of _Gordiodrilus_ occurs, and an obviously introduced _Ocnerodrilus_.

It is among the Geoscolecidae that the most characteristic forms are met with. These belong exclusively to a genus of the Microchaetinae, _Kynotus_, which is found nowhere else but in Madagascar, where it is represented by at least twelve different species.

We have therefore in Madagascar and the surrounding islands only two peculiar genera, only four genera which can be regarded as endemic, and only about seventeen peculiar species.

Passing eastward and crossing the Indian Ocean we come to the Continent of Asia, and we shall first direct attention to the peninsula of India and adjacent parts of Burmah and the island of Ceylon, of which there has been accumulated a great deal of knowledge concerning the Oligochaetous fauna.

This quarter of the globe differs quite as much from any that have been hitherto considered as they do among themselves. We have left behind us the Geoscolecidae with the exception of the ubiquitous and clearly peregrine _Pontoscolex_, and the genus _Glyphidrilus_, which, being aquatic at times, is perhaps hardly to be considered in the present survey.

We have also in this Indian region the equally ubiquitous _Eudrilus eugeniae_ which need not of course detain us further. The Lumbricidae are for the most part of European forms with the exception of _Helodrilus indicus_ conceivably an actual inhabitant of India. It is among the Megascolecidae that the vast majority of the forms endemic in India are to be found. We shall take this family according to its sub-families. In the first place we note that the sub-family Acanthodrilinae is totally unrepresented. The large sub-family Megascolecinae has very numerous representatives. Of the genus _Megascolex_ itself there are some 30 species, of which, however, two or three are looked upon as varieties. Of the allied genus _Notoscolex_ there are ten species and of _Perionyx_ about 13. The genera _Megascolides_, _Diporochaeta_, _Spenceriella_ and _Woodwardia_ have only six species between them of which three belong to _Megascolides_. _Plutellus_ has five species in this region. _Lampito_, which is a widely spread form with but one species _L. mauritii_, may or may not find here its original home. It also occurs in Africa and Madagascar. _Pheretima_ is represented by no less than 12 species, of which at any rate the very great majority are peregrine forms, and not to be safely regarded as forming an integral part of the fauna of the Indian peninsula and adjoining countries.

Of the sub-family Octochaetinae the type genus _Octochaetus_ has ten species in this region and _Eutyphoeus_, which is restricted to the region, has 15 species or perhaps rather more. _Hoplochaetella_ has but one. Of the Trigastrinae there are four or five examples of the genus _Dichogaster_ which occur within the region now under consideration; but it is doubtful whether they are truly indigenous. On the other hand _Eudichogaster_, closely allied both to _Dichogaster_ and _Trigaster_, seems to be confined to this part of the world where it is represented by five species. Finally we come to the last sub-family--that of the Ocnerodrilinae, which is represented by a species apiece of the genera _Ocnerodrilus_, _Nematogenia_ and _Gordiodrilus_. The latter species _G. travancorensis_ is alone to be regarded as endemic and it is very near to the African _G. zanzibaricus_, described some years since by the present author.

The remaining family of terricolous Oligochaeta found in India is the family Moniligastridae which is practically limited to this part of the world and consists of at least twenty species distributed among the genera _Moniligaster_, _Eupolygaster_, _Desmogaster_ and _Drawida_, the majority belonging to the last-named genus.

This quarter of the globe is therefore inhabited by 18 genera which are certainly truly endemic, and which comprise between them about 120 species. But only four or five genera are peculiar.

The remainder of the Asiatic Continent is not very well explored with regard to its earthworm inhabitants. It seems clear however that the southern and coastal region of China and Japan with the Malay peninsula are really continuous with the mass of islands which lie between India and Australia and form together a tract of land which is characterised by an Oligochaetous fauna differing from both that of India on the one hand and Australia on the other. We shall therefore consider this huge portion of the globe as one region comparable to the other divisions that have been hitherto considered. With reference to the Lumbricidae and Geoscolecidae the same remarks may be made as in the case of India. The indigenous forms of the latter family are to be looked upon as outside of the present survey since they are largely or entirely aquatic forms. _Pontoscolex corethrurus_, and _Eudrilus eugeniae_, need not detain us for reasons already amply stated. We now come to the great family Megascolecidae. Of this family the genus _Pheretima_ stands at the head; and of the 200 or so species that have been or can be assigned to this genus all, with merely two or three exceptions, are natives of the Eastern Archipelago and adjoining mainlands of Asia. Of other Megascolecinae the region has yielded the following genera. In Java one species of _Woodwardia_ (_W. javanica_) has lately been described. It is regarded by Michaelsen however as doubtfully indigenous. And the same remark may be made of _Perionyx_. _Plionogaster_, however, with four or five species, is limited, as far as our present knowledge goes, to the Philippines and to neighbouring islands. The Acanthodrilinae and Octochaetinae are totally absent from this part of the world, there being no record even of peregrine species of these sub-families. The sub-family Trigastrinae is not however unrepresented; for of _Dichogaster_ several species occur, such as _D. malayana_ and _D. saliens_. But these are by no means certainly to be looked upon as real natives of the situations within this area where they occur. This completes the scanty list of genera found in the region under consideration; for one Moniligastrid (_M. barwelli_) is hardly to be looked upon as indigenous. We have therefore to record here but five genera, of which only two are certainly indigenous and probably also confined to the region; they contain between them certainly two hundred species.

We next come to the Continent of Australia. The earthworm fauna is again quite without Geoscolecidae and of course Lumbricidae. As to the former there are not even doubtful cases like _Glyphidrilus_ of the East; for we find only recorded _Pontoscolex corethrurus_, a species concerning whose extraordinary powers of migration there is no possible doubt. The same may be said of _Eudrilus_ also recorded from Australia. Here the Megascolecidae are as conspicuous as in the old world generally. We find, however, a great many members of the sub-family Acanthodrilinae. Of the antarctic genus _Notiodrilus_ there are some six species. _Microscolex_ occurs; but the real habitat of this genus is very doubtful. _Diplotrema_, with one species, _D. fragilis_, is not only indigenous to, but confined to, Australia.

The most prevalent sub-family is that of the Megascolecinae. Of the genus _Pheretima_ there are two species which may or may not be truly indigenous. Of _Plutellus_ there are forty species; there are over thirty of _Diporochaeta_, while _Notoscolex_ (with which Dr Michaelsen associates _Digaster_, _Didymogaster_, _Perissogaster_) includes more than forty species, _Fletcherodrilus_ has but one species, _Megascolex_ has seventy species, _Woodwardia_ sixteen, _Spenceriella_ five, and _Megascolides_ seventeen. There are four species of _Perionyx_ which were at one time regarded by Michaelsen as necessitating a new but allied genus _Perionychella_; the two are now merged. Thus there are not far short of 150 species and eleven genera represented, of which only two are limited to Australia.

Having completed the survey of the central and southern land masses of the globe we next direct attention to the northern land masses, viz. North and Central America on the one hand, and Europe and northern Asia on the other. With regard to America we find besides many species of Lumbricidae the genera _Notiodrilus_, _Microscolex_ among the Acanthodrilinae, _Megascolides_ and _Plutellus_ of the Megascolecinae, no member at all of the Octochaetinae, a considerable number of species of _Ocnerodrilus_ and sub-genera belonging to the Ocnerodrilinae, a good many species of _Dichogaster_ and at least one of _Trigaster_ among the Trigastrinae, while one sub-family, that of the Diplocardiinae, is only found here and contains two genera _Diplocardia_ and _Zapotecia_ with quite ten species between them of which only one belongs to the last-named genus. There are no Geoscolecids (except the chiefly aquatic _Sparganophilus_); this family stops short in the West Indies where their presence has been briefly referred to in considering the worms of South America. The vast majority of the genera enumerated here are only found in the warmer parts of the North American continent. We have therefore in this division of the world some nine genera of which at least one, viz. _Diplocardia_ (and its close ally, hardly perhaps to be separated, _Zapotecia_), is confined to it, while _Trigaster_ only extends as far south as to the West Indies.

Europe and northern Asia, of which Europe alone and certain limited tracts of Asia are at all known, contain all the genera of the family Lumbricidae which are (according to Michaelsen) _Eiseniella_, _Eisenia_, _Helodrilus_, _Octolasium_, _Lumbricus_ with various sub-genera of _Helodrilus_, such as _Dendrobaena_ and _Allolobophora_. Besides these forms, which amount to at least 130 species, we find the genus _Hormogaster_, with two species, the only genus of the Geoscolecid sub-family Hormogastrinae; there is also a species apiece of the genera _Criodrilus_ and _Sparganophilus_ (sub-family Criodrilinae). But as these are at least largely aquatic they come under another set of rules and are not important in the present survey of the earthworms of the world. It will be thus seen that with these two last exceptions the area in question contains but six genera of which _all_ are peculiar.

We have now completed the survey of the principal land-masses of the globe. We shall conclude with a reference to one of the largest islands of the world, viz. New Zealand, with which will be included a few outlying islands such as the Aucklands, Snares Island, etc. The reason for not ignoring these islands as we have ignored certain other islands of large size, such as Japan, will be apparent from the peculiarity of the earthworm fauna which they show. From New Zealand the Moniligastridae, Geoscolecidae, Lumbricidae, and, of course, the Eudrilidae, are absent, save the ubiquitous _Eudrilus_. The only family of earthworms which is here represented is that of the Megascolecidae. Of this family the Acanthodrilinae are very well represented. We have at any rate seven species of the genus _Notiodrilus_ of which the bulk are from the small adjacent islands and not from the mainland. The genus _Rhododrilus_ with nine species is actually limited to the New Zealand group and so is an allied genus consisting of two species only, viz. _Leptodrilus_. This latter genus is confined, so far as present information goes, to the Auckland and Campbell islands. _Dinodriloides_ with two species is also limited to New Zealand and to the North Island. _Maoridrilus_ with some ten species is another native and restricted genus. So too is the allied _Plagiochaeta_ with numerous setae on each segment but with the alternating and single nephridial pores of _Maoridrilus_. There are several species of _Plagiochaeta_ of which one has been lately regarded by Dr Michaelsen as really falling within the otherwise Indian genus _Hoplochaetella_, while for another he has formed the genus _Pereiodrilus_. _Neodrilus_ with but one species _N. monocystis_ is another peculiar New Zealand genus. The family Octochaetinae contains only four genera, of which one, viz. _Dinodrilus_ (with four species), is limited to New Zealand, while _Octochaetus_ has about five representatives. _Hoplochaetella_ (if Dr Michaelsen's surmise referred to above be correct) has one species in New Zealand. The Megascolecinae are less numerous than the Acanthodrilinae, but there are ten species of the genus _Megascolides_ (which includes Benham's genus _Tokea_), perhaps seven species of _Diporochaeta_, and two other species which Michaelsen has removed from the genus _Diporochaeta_ and placed in _Spenceriella_. One _Plutellus_ (which however may have been introduced) completes the New Zealand Megascolecines. We have therefore in this part of the world fifteen genera including between them some 58 species; eight of the genera are peculiar to the islands.

From this brief statement of facts some inferences of interest can be drawn. It is in the first place plain that every part of the world except the extreme north and south has a considerable fauna of earthworms. The one exception would appear to be the northern part of the North American continent. Here we meet with members of the family Lumbricidae which are however species that are met with in the Euro-Asiatic province and are thus to be regarded as possibly later immigrants introduced probably by man. Thus temperature short of a constantly frozen condition of the ground is not a bar to the existence of earthworms. Even a freezing of the ground for lengthy periods is not a complete obstacle to the existence of those Annelids; for I have myself received examples of Lumbricidae from the arctic island of Kolguev. Moreover the temperate regions would seem to be as fully populated in the way of individuals, and even of species, as are the tropical regions. Indeed as to individuals it seems that the temperate regions are more fully supplied than much of the tropics. This however is not quite the object of the present section to discuss. We are here concerned with the relative frequency of genera and species. There are according to a recent estimate of the Rev. H. Friend some forty species recognisable in Great Britain. And as already has been stated the earthworms of Europe amount to perhaps 130,--at any rate well over one hundred. In tropical America there are hardly more. But in the latter case the number of genera is very greatly in excess of that of Europe. We cannot however say that an abundance of generic types is quite characteristic of the tropics. For the Eastern Archipelago, though rich in species, is but poor in genera, not possessing more than half a dozen or so. And on the other hand the temperate climate of New Zealand has produced a very considerable series of genera, much more than those of the islands of the East and nearly as many as those of, for instance, Central America and the West Indies.

This conclusion is in its turn contradicted by the conditions observable in Chili and the temperate regions of South America, where the number of species is large but the number of genera small. In short no general laws, in the present state of our knowledge, can be laid down as to the connection between species and genera on the one hand and climatic conditions on the other. In this department of our subject we cannot do more than has already been done, _i.e._ to state the actual facts. One is tempted in comparing the rich fauna of tropical Africa with the very limited fauna of Madagascar to associate a richness of types with extent of land surface. In the two cases cited this conclusion is obvious. It may also be extended--if we confine ourselves to species and not to genera. For the two great islands of New Zealand have not between them more than fifty species of earthworms, while Australia has four or five times that number. It will be noticed however that we cannot associate poverty of generic differentiation with limited land masses; for New Zealand has a large number of generic types, very many more than the huge Euro-Asiatic tract of continent.

THE RANGE OF GENERA.

We have seen, and shall again refer to the fact, that individual species of earthworms have not as a rule a range over a great extent of country, save only in those cases such as _Pheretima heterochaeta_ which belong to that physiological section of these worms called 'peregrine' forms; these appear to possess some means of extending their range by the assistance of man which is denied to other forms. Apart from these instances, which do not come under the present category, it is only _Lumbricus_ and its immediate allies, _Helodrilus_, etc., of which certain species are found to exist over wide tracts of land. There are however many genera which have a wide range and which may be contrasted with others in which the range is very limited. The two extremes are moreover connected by forms with an intermediate range. There is no doubt whatever that the genus with the widest range is _Notiodrilus_ of which species are found throughout the antarctic region, viz., in Patagonia, the islands of the Antarctic Ocean, the Cape of Good Hope, New Zealand, and also further to the north, sometimes even to and beyond the tropics in America, Australia, and Africa. There is no other genus of which the genuine extension (_i.e._ not in any way due to man) is so great as this genus _Notiodrilus_. And this fact gains much significance from the now generally accepted view that in its anatomical structure _Notiodrilus_ comes near to the original type of earthworm.

Perhaps the next most widely distributed genus is _Helodrilus_ of the family Lumbricidae which occupies Europe and Asia to the extreme east, and is thought also to be indigenous to certain parts of North America. But this range, though equally wide perhaps in mileage, is less impressive than that of _Notiodrilus_, since the land areas inhabited by the genus are continuous--almost so if we accept North America as its real habitat. Here we have a case precisely the opposite of that of _Notiodrilus_; for while there are reasons for regarding _Notiodrilus_ as an ancient form of Lumbricid, there are equally good reasons for regarding the Lumbricidae as the most modern family of earthworms.

To find other instances of widely spread genera we must recur to the great family Megascolecidae. There are practically no Geoscolecidae which have a really extensive range. The only instances are _Criodrilus_ and its ally _Sparganophilus_ which occur in America, whether North or South, and in Europe; but as these forms are at least largely aquatic the facts are not quite comparable with those now under consideration.

The genus _Dichogaster_ (which includes as synonyms _Benhamia_, _Millsonia_, _Microdrilus_) is unquestionably indigenous to tropical Africa and certain parts of America including the West Indies. It has been also met with in the East; but as the species there occurring, such as for example the species originally described by myself as _Microdrilus saliens_, are of small size, an accidental introduction is quite possible, and it is by no means certain that it has not occurred. In any case the genus is known to possess species which are undoubtedly to be reckoned among peregrine forms--such as _D. bolavi_, which has turned up in Europe. _Gordiodrilus_ and also _Ocnerodrilus_ with its sub-genera have very much the same range as has _Dichogaster_. It is to be noted however that these forms are circumtropical, and that their distribution is thus less continuous than that of _Notiodrilus_; they do not however show the markedly discontinuous range of certain other genera of Megascolecidae. For instance _Octochaetus_ is well known from New Zealand, and, not occurring in the intermediate tracts, is again met with in India. _Hoplochaetella_ is believed by Michaelsen to present us with another precisely similar instance. Then also the genera _Woodwardia_ and _Notoscolex_ are to be found in Australia and again (absent from the immense tract lying in between) in Ceylon. _Megascolex_ has much the same range, showing also this marked and remarkable discontinuity. Stranger still, perhaps, is the range of _Plutellus_ and _Megascolides_, of which the former, chiefly found in Australia and Tasmania, not only extends its habitat to Ceylon but also to North America; it is there represented by Eisen's species _Argilophilus marmoratus_, referred by him, and not unnaturally, to a distinct genus, but placed by Michaelsen in _Plutellus_. _Megascolides_ is Australian and from the North Island of New Zealand, where its species were regarded by Benham as of a distinct genus, _Tokea_. There is also one form, _Megascolides americanus_, in the western region of North America.

The two genera _Yagansia_ and _Chilota_, closely related to _Notiodrilus_, have a range which is short of that of _Notiodrilus_, and we shall see later that there are reasons for regarding these genera as derived from _Notiodrilus_. They are met with only in the south of South America, and in the Cape of Good Hope region.

The range of _Microscolex_ seems to be much the same as that of _Notiodrilus_; but it is a little uncertain how far the genus is really autochthonous in the countries where it occurs; and in any case it differs from _Notiodrilus_ in occurring in Europe, where the species has been named for a long time _M. phosphoreus_. We do not positively know whether this is 'peregrine' in Europe or not.

The range of the antarctic Acanthodrilinae is in a sense continuous; for they argue the former northward extension of the antarctic continent and in any case they occupy neighbouring land masses. In _Octochaetus_ and _Plutellus_ the case is different and one of real discontinuity. There are however cases of wide range which is also actually continuous and such is afforded by the genus _Pheretima_. This genus appears to be possibly indigenous to Australia; in any case it reaches from the Solomon Islands on the east to India towards the west, being found in all intermediate continents, while it reaches Japan on the north side of this large area.

There are other genera which extend their range over a considerable area, but which are not so widely distributed as these which we have just been considering. Thus _Diporochaeta_ is chiefly Australian but also reaches even the South Island of New Zealand and the southward lying antarctic islands. _Desmogaster_ and _Eupolygaster_ among the Moniligastridae range from Burmah in the east to Sumatra and Borneo further east, though they are not recorded from intermediate islands. _Perionyx_ is found in Burmah, India, Zanzibar, Sumatra, and Java. There are other examples of genera which have much the same range as those enumerated. Finally there are those which are confined to one land mass and very often to a restricted region of that. Thus _Kynotus_ is confined to Madagascar, all the genera of Eudrilidae to tropical Africa, some of them, _e.g._ _Beddardiella_ and _Euscolex_, to very limited tracts, others to wider or less wide areas in that continent. _Maoridrilus_ is only found in New Zealand, to the South Island of which also is confined the genus _Neodrilus_. To the Cape region of Africa is limited _Microchaetus_; and to a belt running across the northern part of the tropical region and extending down the Nile, the remarkable, partly aquatic, _Alma_.

As a kind of appendix to these facts and conclusions we shall next deal with certain widely spread forms that have been already referred to, with the range of different genera over great land masses of the world, and with the earthworms of oceanic islands.