d. The heart in its chamber, with the outgoing vessels as far as

dissected. Use arrows to show direction of circulation.

e. A copy of some good diagram or chart which illustrates the heart of the fish with the connecting veins and arteries.

Fishes: A General Review and Library Exercise

1. Food and the feeding habits of young and of adult fishes.

2. The diet and habits of cod; lantern-fish; swordfish; ramora; hagfish; angler; gar-pike; sturgeon; shark; sawfish; paddle-fish.

3. The variations, real or apparent, in the breathing habits of the porcupine-fish; the climbing-fish; the lung-fish.

4. Peculiarities in swimming as seen in the flying-fish; the flounder; the sea-horse.

5. Intensity of sound under water, and the corresponding structure of the fish's ear.

6. Light and sight under water (as in 5).

7. Protection of fishes: sting-ray; torpedo; coral-fish; sturgeon; lava-fish; swordfish; sawfish; pipefish.

8. The social instinct of fishes, and "schools."

9. The breeding habits of salmon; eel; stickle-back; sturgeon; whitefish; shark; sea-horse; sunfish.

10. The fishing industries of the Great Lakes or of the cold oceans, with a list of the fishes caught and their values.

11. Fish nets and traps: seine; gill-net; pound-net; trawl, French or English; fish-wheel; fish-weir; spear; dip-net; set-line; spoon; fly.

12. The U.S. Bureau of Fisheries: its locations, its problems, and its methods.

13. The State Fish Commission, as above.

14. Game and fish laws; their purpose and their enforcement.

15. Game fish of the fresh waters; trout, bass, pickerel, and muskellunge.

16. Game fish of the ocean: tarpon, tuna, sea-bass, swordfish, and bluefish.

17. Fish as food.

18. Fish diet and leprosy.

19. Fish diet and parasitic worms.

20. Fish nuisances: carp, catfish, and dogfish.

21. Commercial products of fishes, their preparation and their uses: caviar, shagreen, cod liver oil, isinglass, and glue.

22. The geographic distribution of fishes, with means of dispersal and restriction.

23. The faunal regions of the lake (or ocean), with characteristic forms.

24. Fishes of ancient times; of the Devonian period.

25. The story of the early life of Louis Agassiz; of D. S. Jordan; of C. H. Eigenmann; of Bashford Dean.

26. Goldfish: their origin; how to care for them.

27. Fashions in fish tails, old and new.

28. Development and variation in scales; fashions in scales.

29. The common orders of fishes, with examples.

Primitive Chordates

_Materials._

An acorn-tongued worm, a lancelet, a lamprey, a shark, and a perch. If individual specimens are not available, the pupil's text-book and charts are to be used.

_Observations._

_Acorn-tongued worm_: Notice the very simple form and structure of the symmetrical body, the "proboscis," the collar surrounding the neck with its simple rod of cartilage, the marks of internal gills and gill slits extending some distance along the body, and the presence or absence of sense organs. The acorn-tongued worm (_Balanoglossus_) lives in the sand of the seashore and in shallow water in temperate and tropical regions.

_Lancelet_: Observe the form of the body, of the fin, and of the mouth; note the presence or absence of sense organs, and find out the number of gills or gill slits. The lancelet (_Amphioxus_) is similar in habit to the acorn-tongued worm. By day it lies buried with only the mouth exposed, but at night it swims actively about. It is somewhat more confined to the tropics.

_Lamprey_: Observe here also the primitive or unspecialized form of the body, of the fin, of the jawless mouth, the number of gill slits, and the sense organs.

_Shark_: Examine the body, noting its form and differentiation into regions, its covering, its fins, mouth, gill slits, and sense organs.

_Perch_: If you have not already studied the bony fish, the points suggested for the shark will be sufficient for this exercise.

In each case, find out the condition of the skeleton.

_Questions._

1. Which of these animals seem most simple in form, and which most complex? Give a reason for your answer.

2. Give the stages which show how the fold of skin develops into separate fins.

3. How does the number of gills and gill slits change in the series? (Give definite numbers.) How may the reduction in the number of gills be compensated for in the amount of surface exposed for the exchange of gases in breathing?

4. How is protection afforded the delicate structure of the gills in the final form?

5. Give the stages in the formation of a definite, symmetrical mouth with jaws of equal size.

6. The presence of sense organs may be taken to indicate that there is an organ of control, or brain. How is the development of this organ like or unlike that of the other structures in the series?

7. For the developing brain and nervous system what protection and support is afforded in each case?

The foregoing questions may be answered in tabular form by arranging the names of the animals in a line and the questions in a column.

_Suggested drawings._

a. Acorn-tongued worm, × 1.

b. Lancelet, × 1.

c. Lamprey, × 1/2.

d. Shark: 1, head as far as the pectoral fins; 2, the tail.

e. Perch, as directed for shark.

#B. STUDIES OF AMPHIBIA#

#Progress from Water-living Animals to Land-living Animals#

The Living Frog or Toad

_To show how an Animal may be adapted to both Land and Water Life_

_Materials._

Living frogs in small cages or aquaria; living toads; some pungent liquid, as ammonia.

_Observations._

_The Body._

1. Contrast the body of the frog with that of the fish as to regions, shape, and compactness. How do you account for the differences?

_Locomotion._

2. What kinds of locomotion can a frog use? Why is it difficult for a frog to crawl or walk? How far can a frog jump? How are swimming and jumping accomplished? What do you think is the use of the "hump" on the back?

3. Identify in the legs the thigh, shank, ankle, foot, toes, and web, and in the arm, the upper arm, forearm, wrist, hand, and fingers. State in detail the differences in structure and in position between the fore and hind limbs. How do you account for these differences?

_Feeding._

4. Induce a frog or toad to eat by dangling food, such as a piece of raw meat or meal worms, small earthworms, etc., before it. How does it seize the food? What will it eat? How is the mouth adapted to this manner of feeding?

_Respiration._

5. The frog has no diaphragm, and therefore no chest cavity; watch very carefully the movements of the mouth, the nostrils, the throat, and the sides of the body to determine how the problem of breathing (how the air is gotten into and out of the lungs) without a diaphragm is solved. Write a detailed account of the frog's method of breathing which shall explain just how the air is forced into the lungs.

6. What would be the effect of propping open the mouth of the frog? Why? Does the frog breathe in the usual manner while under the water? If not, how do you explain its ability to remain under water for a long period of time?

_Sense Organs._

7. Investigate the efficiency of the five special senses in the frog by devising experiments to test each sense; as, for example, giving a frog its liberty on the floor and trying to catch it again, to test the sense of sight. Write an account of your experiments and their results. Which of the senses is best developed? Give reasons for your answer.

8. Compare the eye of the frog with respect to its shape, movements, parts, and protective structures with that of the fish. In what respects are they similar? in what respects different? Why should they differ?

9. Where are the frogs' ears located? What do you think of the efficiency of an eardrum situated on the surface of the body? Why?

10. The frog has certain other responses. Try turning the jar or cage containing a frog around to face the frog in another direction. What happens? How do you explain this response on the basis of use? What other responses have you noticed?

_Protection._

11. Has the frog an exoskeleton? Describe the color scheme of the frog and explain how it may be protective. Why are frogs brighter in spring than in fall?

12. Why do frogs usually live near water? Do they ever leave the vicinity of streams? If so, when?

_Summary._

In what ways is the frog adapted to water life? In what ways to life on land? In what respects do toads differ from frogs?

The Frog's Mouth

_Materials._

Preserved or freshly killed frogs in dishes or shallow pans of water; forceps and a bristle.

_Observations._

Open the frog's mouth as widely as possible and, if necessary, insert a splinter to hold the jaws apart. Identify the following structures:--

_Tongue._ Draw it forward until the free end extends from the mouth and is outspread; observe its form, extent, and attachment.

_Teeth._ Find those on the jaws and on the roof of the mouth.

_Nostrils._ Push the bristle inward through a nostril to determine its direction and extent.

_Vocal cords._ These form a hard white mass in the floor of the mouth, well back behind the tongue.

_Glottis_, the slit inclosed between the vocal cords, opening into the trachea.

_Esophagus_, the passage to the stomach, at the posterior end of the mouth.

_Eustachian tubes_, small passages outward to the ears at the junction of the upper and lower jaws.

_Questions._

1. Describe the probable action of the frog's tongue in catching a bug.

2. What advantage can you ascribe to the peculiar mode of attachment of the tongue?

3. Of what use is the notch in the inner end of the tongue? (Note its position when the tongue lies at rest in the mouth.)

4. If the frog chewed its food, how would the existing structure of the nostrils be very inconvenient?

5. Recall either the frog's habit of feeding or the structure of the nostrils. Do you think the nostrils are of much service in smelling? State the reason for your answer.

6. Of what use are the vocal cords and why are they so muscular? Consider their use in sound making and also their condition during swallowing.

7. Of what use are the teeth? Recall the form and use of the fish's teeth.

_Suggested drawings._

a. The mouth, wide open and with tongue extended.

b. A diagram showing the path of air and of food through the frog's mouth.

The Organs of Digestion, Absorption, and Excretion

_Materials._

Freshly killed or preserved frogs in dishes or shallow pans of water, forceps, and, if the pupil is to do any dissecting, scissors.

_Directions and Observations._

The specimens may have been opened by the teacher, or may be dissected by the pupil as follows:--

Placing the frog on its back, with forceps firmly grasp the skin of the abdomen and the muscles beneath, just in front of the hind legs, and with the scissors cut straight forward in the middle line until the floor of the mouth is reached; this will separate the arms. Care must be taken not to cut too deeply, but this may be avoided by keeping the skin uplifted. Now cut sidewise in front of each hind leg in order that the body wall may be laid aside. Under the arms the heart will be seen; it will be studied as a part of the circulatory system.

* * * * *

Identify the following organs:--

_Liver_, the large red or brown mass, consisting of several divisions and lying close up under the arms.

_Bile sac_, small, green, and between the liver lobes.

_Alimentary canal._

1. _Mouth._

2. _Esophagus._

3. _Stomach_, the elongated, light-colored, firm, and muscular portion.

4. _Small intestine_, a slender, more or less closely coiled, tubular portion.

5. _Large intestine_, a thin-walled enlargement at the posterior end of the canal.

6. _Duodenum._ This is a muscular portion of the small intestine immediately following the stomach, against which it is folded.

_Pancreas_, a yellowish, pulpy mass lying in the fold between the stomach and the duodenum.

_Spleen_, a dark red globule, usually smaller than a pea, lying nearly free among the folds of the small intestine.

_Fat bodies_, yellow fringe-like structures, sometimes found near the stomach.

_Kidneys_, a pair of elongated dark red organs, behind the spleen and against the back. Note their numerous blood vessels. Possibly the _ureters_, or urinal ducts, can be discovered and traced to their junction with the _bladder_, a clear membranous sac in the posterior extremity of the body cavity.

_Peritoneum_, a thin membrane lining the body cavity and attaching the vital organs to the backbone.

_Note._--Specimens secured in late fall, winter, or early spring may contain, if female, a large number of dark-colored eggs; or if male, two white testes, located near the kidneys and similar to them in form, though smaller.

_Questions._

1. Name the parts of the frog's alimentary canal.

2. Name the glands or organs which are accessory to the canal.

3. How long is the esophagus? How does the presence or absence of a neck affect the esophagus?

4. How does the thickness of the stomach wall compare with that of the intestine, and how do you account for the difference?

5. Measure the length of the trunk of the frog's body and that of the outstretched alimentary canal. How many times the length of the one is that of the other? How does this ratio compare with that of an herbivorous animal? (The sheep's food canal is about thirty-two times the length of its body.)

6. What is the color of the bile, as seen through the walls of the bile sac? This color is characteristic of carnivorous animals; in herbivorous forms it is yellow. Find its color in some omnivorous form, as man.

7. Name the organs concerned in excretion.

8. What holds the internal organs in place, and from what are they suspended?

9. The spleen is called a "ductless gland." Give its function, and explain why a duct is not necessary to it.

10. Since the frog swallows its food alive and entire, what work must the stomach do? What digestive organs would be absent from the mouth, or else poorly developed?

11. Since the frog is carnivorous, what digestive ferments are probably present, and what ones absent from the alimentary canal?

12. Fat bodies are largest in the fall, and are rarely found in the spring. How can you account for this?

13. When through with the general study of the alimentary canal, you may open the stomach by cutting it lengthwise. Describe the character of the stomach lining as to folds and villi, stating the advantage of each being present and the reason for the direction of the folds. Tell how the food is propelled onward through the alimentary canal. Give the scientific name for this action.

_Suggested drawings._

a. The viscera (internal organs) undisturbed.

b. The alimentary canal extended.

c. The excretory system.

The Organs of Circulation and Respiration of the Frog

_Materials._

The materials used in this exercise are the same as those used in the preceding exercise.

_Observations._

The pupil should identify the following structures:--

_Pericardium_, a membrane that surrounds the heart and, in the case of the frog, separates the body cavity into two portions, the _abdomen_ and the _pericardial_ chamber.

_Heart_, lying between the shoulders and in front of the false diaphragm. It is conical in form and composed of three chambers.

_Ventricle_, the pink, conical, and muscular portion of the heart, pointing backward and outward.

_Auricles_, right and left. These are anterior and dorsal to the ventricle, thin, membranous, and dark-colored.

_Arterial trunk_, the single large blood vessel, usually empty of blood, and white. Note its origin and trace it as far as possible, at least until you see it divide to encircle the throat.

_Sinus venosus_, a large membranous sac dorsal to the heart and connected with the right auricle.

_Lungs_, two small oblong, pink, spongy sacs, lying between and behind the shoulders.

The pupil may also identify the following structures if a specimen is available which has the blood vessels injected.

_Conus arteriosus_, or "arterial trunk," a large artery passing obliquely forward from the ventricle, and dividing into three branches on each side.

_Carotid arteries_, the first branches of the conus, to the head and neck.

_Aortas_, the second branches of the conus, to the dorsal region.

_Pulmocutaneous arteries_, the third branches of the conus, to the lungs and skin.

_Dorsal aorta_, the large artery along the back, formed by the union of the two aortas.

_Iliac_, or _femoral arteries_, the two posterior divisions of the dorsal aorta, supplying the legs.

_Posterior_ (ascending) _vena cava_, a large vein close to the dorsal aorta, passing forward from the kidneys.

_Hepatic veins_, large veins connecting the liver with the posterior vena cava.

_Anterior_ (descending) _venæ cavæ_, large veins formed by the junction of the veins from the arm, neck, and head on the right and left sides.

_Subclavian veins_, from the arms.

_Jugular veins_, from the neck.

_Questions._

1. Of how many chambers does the frog's heart consist? Name them, and describe them as to size, color, and structure.

2. Which chamber receives blood from the body, and which receives blood from the lungs?

3. Name the large arteries and give the regions which they supply. Name the large veins and give the regions from which they come.

4. Describe the lungs as to size, both when inflated and when uninflated. Describe their color; entirety or subdivision; texture.

5. In the inflated lung, notice the interior partitions or chambers, which are called _vesicles_. How do they affect the amount of surface exposed for gas exchange in breathing?

6. Measuring the lung collapsed and again when inflated, calculate its approximate volume in each case and state how much air it may take in during an inspiration.

7. Describe the diaphragm and state its probable use as a factor in respiration or as a partition.

_Advanced questions._

8. Apparently the pure and the impure blood must commingle upon entering the single ventricle, but by a simple device this scarcely occurs. How would such commingling affect the purity of the blood as it reached the tissues, and hence affect waste removal, oxidation, body temperature, activity, and intelligence?

9. What are the chambers of the fish's heart? of the mammalian (human) heart? How may the heart of the frog be regarded as intermediate between these others? How and where might the growth of a partition within it bring about the higher structure? (This actually occurs in certain reptiles.)

10. The lungs are said to be outgrowths of the alimentary canal. Explain how their connection would tend to show this.

_Suggested drawings._

a. The heart and lungs in their normal position.

b. The circulatory system, as seen in the injected specimen.

c. A copy of the diagram or model of the circulatory system.