PART VI (RODENTIA).

Though very numerous, the parasites of this order are chiefly interesting as embracing those of the hares and rabbits, moles, mice, rats, squirrels, and beavers. Some slight notice, however, will be given of the entozoa of each of the eleven families into which the order may be divided.

The squirrels (_Sciuridæ_) are liable to be infested by the common liver fluke (_F. hepatica_), and also, it is said, by a cysticercus (_C. tenuicollis_). I have never encountered this bladder worm, but in 1864 I described some polycephalous hydatids (_Cœnuri_) which I obtained from the viscera of an American squirrel. I think the host was of the same species (_Sciurus vulpinus_) as that from which Mr Chapman has since obtained an example of Echinorhynchus (_E. moniliformis_). This worm also infests the hamster. A very small female round worm, probably a strongyle, was described by Rudolphi as _Ascaris acutissima_. It infests the cæcum of the common squirrel, in which host a species of tapeworm is tolerably frequent (_Tænia dendritica_). The common European marmot is infested by _T. pectinata_, so abundant in hares and rabbits. I have also noticed it as occurring in the Canadian porcupine (_Hystrix dorsata_). The dormice (_Myoxidæ_) are not much troubled with parasites, at least I have not encountered any in our common _Myoxus avellanarius_. In _M. glis_, however, a tapeworm, and at least one species of strongyle (_S. gracilis_), have been observed. Dujardin described very fully another strongyle (_S. lævis_) from _M. nitela_, from the long-tailed field-mouse (_Mus sylvatica_), and from _Arvicola subterraneus_. The other species are _Trichosoma myoxi nitelæ_, and _Ophiostoma cristatum_ from _Myoxus dryas_, and _M. muscardinus_. The jerboas (_Dipodidæ_), in common with the hamster and several species of true mice, are apt to be infested by _Ascaris tetraptera_; and a small nematoid, apparently immature, was noticed by Otto in the intestines and in the abdominal walls and cavity of _Dipus tetradactylus_. Mice, properly so called, are largely infested, as is also the hamster (_Cricetus vulgaris_), which I include in the _Muridæ_. In addition to the parasites already mentioned, the hamster is infested by _Tænia straminea_. Along with examples of this tapeworm I have received from Dr Murie some acephalocysts found in a hamster which died at the Zoological Gardens.

Flukes exist in the long-tailed field-mouse (_Distoma vitta_ and _D. recurvum_), but I have not seen any in our common mice and rats. However, Dujardin describes a distome (_D. spiculator_) in the brown rat (_Mus decumanus_). One of the tapeworms observed in the mouse (_M. musculus_) is _Tænia pusilla_, also found in the rat (_M. rattus_) and long-tailed field-mouse. The house-mouse likewise harbors _T. microstoma_ and _T. leptocephala_; and an immature cestode has also been seen in the abdomen, probably a species of _Ligula_. Various species of rat also harbor _T. diminuta_. In regard to the round worms one of the most common species is _Ascaris oxyura_. This not only occurs in rats and mice, but also in voles, water-rats, and many other rodents. The rodents’ whipworm (_Trichocephalus nodosus_) is yet more common in the lemmings, rats, voles, and mice; another species (_T. unguiculatus_), taking its place in hares and rabbits, and yet another (_T. affinis_) in the porcupine. Another nematoid, very common in mice, is _Spiroptera obtusa_, occupying the stomach. I have seen a mouse with its abdomen so distended by their presence that the animal could scarcely run along the pathway where it was killed by being trod upon. According to Marchi, the young of this entozoon dwell in the fat surrounding the alimentary canal of the larva of an insect (_Tenebrio molitor_). When noticing the parasites of the cat I referred to Leuckart’s interesting discovery of the relations subsisting between the adult _Olulanus tricuspis_, found in the stomach walls of that feline, and the immature encysted worms, found not only as wanderers in the cat itself but also in the muscles of mice. The olulanised mouse is thus an intermediate host. Rats and mice also play the part of intermediary bearers in the case of two other species of entozoa, namely, _Trichina spiralis_ and _Tænia crassicollis_, the tænioid scolex or larval condition of the cat’s tapeworm being familiarly known as _Cysticercus fasciolaris_. This sexually-immature tapeworm infests many other rodents, especially the voles (_Arvicolidæ_). In regard to _Trichinæ_ it must not be forgotten that their presence in rats is not uncommon in some parts of Europe; and this circumstance may explain the recurrence of trichinosis (first in hogs and then in man) in certain outlying districts. Only in this way can the Cumberland outbreak in this country be accounted for. Here I cannot dwell upon the subject, but in this connection I may observe that Bakody has in a very convincing manner described a new variety or species of Trichina, found by him infesting the walls of the stomach and intestine of rats. In the first instance he detected the worm in association with the ordinary _T. spiralis_, but afterwards separately. He also obtained it in fowls. The species should be called _Trichina Bakodyii_. Possibly the nematodes observed by Colin in 1863 also refer to this worm. They occupied tubercles in the liver of a rat. In regard to the beavers (_Castoridæ_) it appears that they harbor many species of round worms, and also several flukes, but they do not appear to have been very much studied. In Morgan’s work on the American beaver there is a notice in which it is stated that Dr Ely found a very fine filamentous worm 40‴ in length. This does not seem to correspond with _Ascaris castoris_ (Rud.). He also speaks of large numbers of a slender white worm, 3″ to 5″ in length, found in the peritoneal cavity, and referable to the genus _Filaria_. This cannot be confounded with _Trichocephalus castori_ (Rud.). Moreover, he describes a strongyle (_Sclerostoma_) as infesting the colon, and especially the cæcum. These all appear to be new to science. The _Fasciola hepatica_ is occasionally found in the liver, but the most common helminth of beavers is _Amphistoma subtriquetrum_. Specimens of this worm may be seen in the British and Hunterian Museums. As regards the porcupines (_Hystricidæ_) I have already mentioned the occurrence of a tapeworm in the common species. The larval _Pentastoma denticulatum_ has been found by Otto attached to the surface of the lungs, and Redi, about two centuries back, noticed small nematodes lodged in tubercles of the œsophagus. The late C. M. Diesing obtained _Trichocephalus affinis_ from the intestines. So far as I am aware, little or nothing has been said respecting the helminths of the _Octodontidæ_, _Chinchillidæ_, and _Cavidæ_. Like other European investigators I have dissected guinea pigs (_Cavia aperœa_) without finding any parasites; but in Brazil a small species of ascaris (_A. uncinata_) was found by Natterer in this animal and also in the paca (_Cœlogenys paca_). The agoutis (_Dasyprocta_) harbor _Trichocephalus gracilis_.

The entozoa of the duplicidentate rodents (_Leporidæ_) acquire importance from the fact of their abundance and from the intimate relation which some of them bear to parasites infesting the dog and other animals. Thus, the two commonest kinds of fluke infesting cattle (_Fasc. hepatica_ and _Dist. lanceolatum_) also attack hares and rabbits; the former parasite often producing the rot disease, which is almost as fatal to the rodents as it is to the ruminants. Mutual infection occasionally results from this circumstance by the distribution of germs. All experiment-conducting helminthologists have reared _Tænia serrata_ from the _Cysticercus pisiformis_; nevertheless, several English Manuals of Zoology persist in propagating the old error of Von Siebold, who supposed he had reared this tapeworm by the administration of Cœnuri. So far as I am aware, no feeding experiments have been conducted with the Cœnuri of rabbits (_C. cuniculi_). These bladderworms infest the soft parts of the body, often producing tumours having a very unsightly appearance. For details I must refer to the papers quoted below. The Norfolk warreners call the infested hosts “bladdery rabbits.” Though apparently most abundant in the eastern counties of England, these diseased rabbits are by no means confined to that quarter. Through Mr Alston’s help I have received specimens of _Cœnurus cuniculi_ from Ayrshire, Scotland. Probably this form of Cœnurus occurs wherever rabbits live. In Italy a case is recorded by Perroncito from the abdominal cavity of a rabbit (_coniglio_). Every experimenter is more or less familiar with the cestode larvæ (_C. pisiformis_) found wandering in the abdominal cavity. These were regarded as flukes by Kuhn (_Monostoma leporis_). I need hardly remark that the developmental and structural changes undergone by these Cysticerci during their residence within the rabbit have been exhaustively followed out and treated of by Leuckart. Without dwelling on this subject, I must in justice add that in this relation the special labors of Küchenmeister, Van Beneden, Haubner, Wagener, Röll, Eschricht, and Möller played no inconspicuous part. My own efforts in 1857, and subsequently, were not unattended with success. It therefore seems to me, without prejudice to the recent experiences of De Sylvestre and others, that further experiments in this immediate connection are unnecessary. As regards the nematodes of leporine rodents, probably the most important is _Strongylus commutatus_. This parasite, like its husk-producing congeners, infesting calves and lambs, occasionally sweeps off great numbers of hares. Such an epizoöty occurred in Thuringia in 1864. The most frequent intestinal parasite of rodents is probably _Oxyuris ambigua_, but _Strong. retortæformis_ is tolerably abundant in the hare, and _Trichocephalus unguiculatus_ is liable to occur in all leporines. I know nothing of the so-called _Strong. strigosus_ of rabbits, but Bellingham found it in Ireland. Olfers and Natterer obtained a small ascaris (_A. veligera_) from _Lepus braziliensis_; but I cannot help thinking that the large measle (_Cysticercus macrocystis_) described by Diesing as three inches in length, and obtained from the same rodent, must either have been _Cœnurus cuniculi_ or else another form of polycephalous hydatid.

In reference to the ectozoa of rodents it may be said that they are very numerous. Acari infest rats and mice, and especially leporines. Thus, in the mouse are found _Sarcoptes notoedre_, Bourguignon, var. _muris_, Mégnin, _Sarc. musculinus_, Koch, and _Myobia musculi_, Claparède. It is not very generally known that wild rabbits are apt to be attacked by the common autumnal spider (_Leptus autumnalis_), whence, as once happened with myself, they may be transferred to the human body. The ears of tame rabbits are sometimes covered with acari, which are easily destroyed by the cautious application of a mixture of carbolic acid and olive oil (one of acid to six of the oil). Rodents also harbor fleas. At a meeting of the Entomological Society in 1875 Mr Vernall showed living specimens from the ears of a rabbit, and Messrs Cole and W. A. Lewis stated that they had obtained fleas from the hedgehog and European marmot respectively.

BIBLIOGRAPHY (No. 47).--_Beneden_ (see Van Beneden below).--_Capelle, J._, Extr. from a letter, in which the author states that he had “found worms of the tænia kind in the liver of sixteen out of eighteen rats,” ‘Med. Commentaries,’ vol. xix, p. 139, 1794; see also ‘Trans. Coll. Phys. of Philad.,’ vol. i, part ii, p. 60, 1793.--_Chapman, H. C._, “Echinorhynchus in Squirrel,” ‘Proc. Acad. Philad.,’ 1874, p. 76.--_Cobbold_, “Note on Cœnurus (from a squirrel),” ‘Proc. Linn. Soc.,’ May 5, 1864.--_Idem_, “On the occurrence of _Tænia pectinata_ in the Porcupine (_Hystrix dorsata_),” in a letter to Dr. Lawson in the ‘Canadian Naturalist and Geologist,’ 1862.--_Idem_, ‘On _T. serrata_,’ &c. (see Bibl. No. 45).--_Colin_, “On the presence of a Nematode Worm in certain Tubercles of the Liver of a Rat,” from ‘Rec. de Méd. Vét.,’ in ‘Edin. Vet. Rev.,’ Oct., 1863.--_Leuckart_, ‘Die Blasenbandwürmer (u. s. w.),’ 1858 (contains numerous details and figs. in ref. to _Cysticercus pisiformis_ and _T. serrata_, &c.).--_Marchi, P._, ‘Mem. della R. Accad. d. Sci. di Torino,’ xxv.--_Peacock_, “Remarks on the Liver of a Mouse with Cysts containing Cysticerci,” ‘Lancet’ and ‘Trans. Path. Soc.,’ 1855.--_Perroncito, E._, “Sopra un caso di Cœnurus (in the abdominal cavity of a rabbit),” ‘Giornale Med. Veter.,’ 1876.--_Siebold_ (see Von Siebold, below).--_Sylvestri, De_, “Experiments with _C. pisiformis_,” ‘Il. Med. Veterinario,’ 1871.--_Van Beneden_ (see Bibl. No. 45).--_Idem_, “On _Sciurus glacialis_ and its Parasites,” from ‘Bull. de l’Acad. de Belgique,’ in ‘Ann. Nat. Hist.,’ vol. xiii, 1854.--_Verrall_, in ‘Proc. Ent. Soc. Lond.,’ Feb. 15, 1875, p. 3.--_Von Siebold_, ‘Ueber die Band-und Blasenwürmer,’ Leipsig, 1854, and Huxley’s edit. for Syd. Soc., 1857.--_Idem_, “Experiments on the Transformation of the Cystoid Worms into Tænias,” from ‘Ann. des Sci. Nat.,’ in ‘Ann. Nat. Hist.,’ vol. x, 1852.--_Idem_, “Helminthology,” trans. by Busk and pub. in ‘Ray Soc. Rep. on Zool.,’ 1843-44, p. 446, London, 1847.--_Idem_, “On the Transformation of _Cysticercus pisiformis_ into _Tænia serrata_,” from ‘Zeitsch. f. w. Zool.,’ in ‘Quart. Journ. Micr. Sci.,’ 1854.