Chapter VI: Vertebrates (1)

#A. STUDIES OF FISHES#

THE LIVING FISH

_Vertebrates adapted to Water Life_

_Materials._

Living goldfishes or other fishes in small aquaria for individual study and a few fishes in a large aquarium where they have considerable freedom of motion.

_Definitions._

_Trunk_, the portion of the body between the head and the tail.

_Compressed_, a term used to describe the shape of the body when it is narrower from side to side than from dorsal to ventral surface. When the opposite is true, the body is said to be _flattened_.

_Median fins_, the unpaired fins situated on the median line, dorsal and ventral, including the tail or _caudal_ fin, the _dorsal_ fin, and the _anal_ fin.

_Paired fins_, fins occurring in pairs of which the more anterior are the _pectoral_ fins and the posterior are the _pelvic_ fins.

_Fin rays_, the framework or skeleton of the fins over which membrane is stretched to form the fins. Fin rays are of two kinds: those composed of _bone_ and those composed of _cartilage_.

_Lateral line_, a sense organ extending along each side of the fish in a line indicated by tubes or perforations in the scales.

_Gills_, respiratory organs adapted for taking oxygen from the water.

_Operculum_, the flaps covering the gills on each side of the head.

_Pigment_, a substance which gives color to an object.

_Observations._

_Locomotion._

1. Watch the fishes in the large aquarium and determine which fins are most used and how they are used (a) in swimming forward, (b) in swimming upward and downward, (c) in maintaining balance, (d) in remaining at rest, and (e) in guiding the movements of the fish.

2. What advantages are there to the fish (a) in the power to open and close the dorsal and anal fins, (b) in having no neck, and (c) in having a compressed form?

3. Enumerate the various ways by which the body of the fish is adapted to rapid movement through the water.

_Feeding._

4. What is the food of the fishes you are studying? Feed them and watch them eat. Why is the upper jaw often called a "lip"? What is the shape and size of the mouth when opened in feeding? Does the fish chew its food? Describe in detail the fishes' method of feeding.

_Respiration._

5. Identify the opercula and the gill openings. Watch the movements of the opercula and mouth, and determine what movements are concerned in breathing and their order. Describe in detail the circulation of water used in breathing and how it is caused.

_Sense Organs._

6. Identify the eyes, nostrils, and lateral line. How many nostrils are there and where located? What is the position and extent of the lateral line?

7. Describe the location of the eyes. What is the shape of the outer surface of the eyes? Why this shape? Can the eyes be moved, _i.e._ can they be rotated, rolled, or retracted? From what direction might an enemy approach without being seen? How would such an enemy be detected?

_Protection._

8. With what protective structures is the body covered? Do they hinder the movements of the fish? What are the advantages of the scale covering of fishes over the shell covering of grasshoppers or crayfishes?

9. In what other ways are the fishes you are studying protected against enemies? Since you cannot account for the red color of goldfishes on the basis of use to the fish, then how do you account for this bright color?

_The Body._

10. What is the symmetry of the fish? Into what regions is the body divided?

_Summary of the study of the living fish._

Enumerate in one column the different adaptations which fit the fish for life in water and in a second column state the special purpose of each adaption.

The External Structure of the Fish

_Materials._

Freshly killed or preserved fish in dishes or shallow pans with enough water to prevent drying. Simple or compound microscopes, forceps, and a bristle.

_Directions._

Examine the fins and identify the membrane and the supporting rods, or _rays_, of bone or cartilage. Notice how the ends of the cartilaginous rays keep the membrane from tearing.

Investigate the scales as to their arrangement, number, and size. Remove a small patch of scales along the lateral line to find how they are attached, where the fish's color is situated, and how access to the sensory organs of the line is permitted. Examine a scale under the microscope.

Observe the eyes and identify the parts similar to those of the human eye: lid, lash, tear-duct, cornea, iris, and pupil.

In front of and between the eyes, find the nostrils. By means of a bristle determine whether these are connected and whether they do or do not open into the mouth or the throat.

_Questions._

1. Make a list of the fins, classifying them according to their structure.

2. Bearing in mind the differences in structure and consequent action,--what can you say regarding the adaptation of the several fins for protection? for rigidity or flexibility in locomotion?

3. State how much of the body is covered with scales, and where the largest and the smallest ones are found.

4. How are the scales arranged with reference to each other? What benefit is derived from this in protection? in locomotion? If you have noticed any mucus or slime upon the body, state its use.

5. Do the scales or the skin bear the pigment? Give the color pattern of the kind of fish used in class. How would this be useful to the fish in its natural home?

6. Describe the structure of a scale and state how it is attached to the skin. In what way is the lateral-line scale specialized?

7. State how, when the fish is swimming, the nostrils catch odors. By means of a diagram, with arrows show the probable direction of the water current through the nose.

8. State which of the structures of your eye are present in the fish's eye, and which are missing. Could a fish weep? wink? How would a fish sleep?

9. Inasmuch as light penetrates water but a little way, so that objects can be distinguished only within about thirty feet, would the fish be nearsighted or farsighted?

_Suggested drawings._

a. A side view of the entire fish, fully labeled.

b. A bony rayed and a cartilaginous rayed fin.

c. A scale, showing its minute structure.

d. A dorsal or a lateral view of the head, showing the sense organs.

The Mouth and the Gills of the Fish

_Materials._

The same materials as those used in the preceding exercise may be used here.

_Directions._

The mouth, its structure and its action, can be seen by pulling the upper jaw upward and forward until the mouth and the gill chambers open fully. Examine the structure and action of the jaws, the tongue, the throat, and the teeth on each jaw and on the roof of the mouth.

Investigate the breathing apparatus from the throat side and from the exterior, noting the number, form, and structure of the gills, their attachment and their protection.

The mouth may be kept open by a short splinter or a ball of paper.

The pupil should identify the following structures:--

1. _Gill_, an organ for breathing the air dissolved in water.

2. _Gill arch_, an arch of bone or cartilage supporting the gills.

3. _Gill filaments_, fringe-like structures attached to the gill arches, forming the gills.

4. _Gill raker_, lateral projections from the gill arches.

5. _Gill-slits_, openings between the gill arches for the passage of water.

6. _Operculum_, the flap-like covering of the gills on each side of the head.

_Questions._

1. Compared with the size of its body, how wide can the fish open its mouth? What do you infer as to the size of its "bite"?

2. Are the jaws rigidly affixed to the skull? Why should they be so attached, or why not?

3. Of how many pieces is the upper jaw composed? the under jaw?

4. Where are the teeth? Judging from their form, size, and situation, what do you think must be their use?

5. Do you think the tongue is used to assist in mastication? in tasting? in speech? in swallowing?

6. How many gills are there, and where are they situated? How are they attached? Which one is not free from the body throughout its length?

7. What probably causes the color of the gill filaments? What is there in their number and texture which fits them for their function?

8. What is the direction of the water current through the gill chamber? Of what use are the gill rakers?

9. How are the gills protected?

_Summary._

Write a complete account of how the fish eats and how it breathes.

_Suggested drawings._

a. A front view of the fish's face, with the mouth fully open.

b. A side view, as above.

c. A ventral view of the head, with both gill-chambers wide open and the gills separated from each other. Indicate currents by arrows.

d. A single gill.

The Alimentary Canal and the Circulatory System of the Fish

_Materials._

Small fresh fish, shallow pans or dishes of water, forceps, and scissors.

_Directions._

If the instructor has not opened the fish previously, this is to be done by the student as follows: On the ventral side, insert the scissors in the vent (in front of the anal fin) and cut straight forward to a point between the opercula. Care must be exercised in opening the chamber about the heart; this lies between the gill chambers.

The various organs, so far as possible, should be carefully drawn out and separated, in order that their structure may be distinguished.

The pupil should identify the following parts:--

1. _Body cavity_, the entire internal space, divided by a membrane, _false diaphragm_, into a large _abdominal cavity_ and a small chamber, _pericardial chamber_, between the gill chambers.

2. _Liver_, a large red or pink mass lying at the front end of the abdominal cavity, and divided into two unequal lobes. The _gall-bladder_, thin-walled and green, may be seen between these lobes.

3. _Alimentary canal._

a. _Mouth._

b. _Esophagus_, in the fish a very short tube.

c. _Stomach_, white and muscular, beginning with a very short
esophagus and ending as a blind sac. If it is much distended,
open it to see what the fish may have eaten.

d. _Small intestine_, thin-walled, tubular, and somewhat coiled.

e. _Large intestine_, a short, thin-walled expansion at the
posterior end of the small intestine; usually less than half an
inch long.

f. _Coeca_, from two to several small pouches attached where the
small intestine leaves the stomach.

4. _Spleen_, a reddish brown _globule_ between the folds of the intestine.

5. _Swim bladder_, an elongated chamber lying against the backbone, partitioned off from the cavity below by a delicate membrane.

6. _Peritoneum_, the delicate, silvery membrane which lines the abdominal cavity and enfolds the viscera. Note its spots of pigment.

7. _Pericardial chamber_, the chamber around the heart; see § 1 above.

8. _Heart._ As the fish is placed belly upward in the pan the _ventricle_ faces you, pink, conical, and muscular. Posterior to it, on the dorsal side, is the _auricle_, a membranous sac.

9. _Ventral aorta_, arising on the anterior surface of the ventricle as a white muscular "cord" (really a tube) which is enlarged close to the heart into a bulb, the _arterial bulb_. You should follow up this aorta until you see it divide right and left to send its branches outward into the gills, the branches being called _gill arteries_.

_Questions._

1. The fish frequently swallows its food alive. Why should the stomach be muscular? Why is it better that the intestine does not leave the stomach at the end opposite the esophagus?

2. Of what use can the coeca be? What structure of the human intestine do you recall that is at all like them in form or use?

3. How many times the length of the body is the length of the alimentary canal? Does this indicate that the fish is compelled to eat a great deal of poor food or that its food is highly nutritious, so that little need be taken?

4. Near which end of the fish's body is the heart? Is this the usual or the unusual condition among animals you know about? What advantages can you think of in this arrangement?

5. What advantages are there in having the heart in a chamber separated from the other vital organs?

6. Of how many chambers does the heart consist? Why should at least one of them be muscular?

7. How many times does the blood pass through the heart in making a complete circuit of the body? Would you call this a single or a double circulation?

8. Does the heart force the blood onward or does it draw blood into itself, _i.e._ is the heart a force pump or is it a suction pump?

9. How is circulation made complete? If the heart is a force pump, is its power sufficient to drive blood through artery, capillary, vein, and into auricle, if the capillaries can stand the pressure, or is another action concerned? If it is a suction pump, why does the blood leave the heart?

_Suggested drawings._

a. The body cavity, with viscera undisturbed.

b. The alimentary canal extended.

c. The anterior end of the fish with the sinus held open, to show the general situation of the parts.

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.

d. A diagram of the respiratory tract from the nostrils to the lungs, by arrows showing the course of the air.

The Nervous System of the Frog

_Materials._

Specimens which have the brain exposed and other specimens whose viscera have been removed so that the spinal nerves can be seen; pans or shallow dishes of water and forceps.

_Observations._

The nerve tissues are generally white in color unless they have been specially treated and stained. The pupil should identify the following structures:--

_A. Brain_, those enlargements of nerve tissue situated in the head and composed of four principal parts, as follows:--

1. _Cerebral hemispheres_, a pair of elongated lobes, the anterior enlargements.

2. _Mid brain_, or _optic lobes_, a pair of large ovoid structures, projecting diagonally forward and sidewise.

3. _Cerebellum_, a slender, transverse ridge, close behind the midbrain.

4. _Medulla_, the anterior end of the spinal cord, widest in front and containing a triangular depression.

(Frequently a pair of smaller enlargements is to be seen in front
of the cerebral hemispheres; they are the _olfactory lobes_, and
from them nerves pass forward to the nasal chamber.)

_B. Spinal cord_, extending along the spine, giving rise to nerves.

_C. Spinal nerves_, ten pairs of nerves which are connected with the cord through dorsal (sensory) and ventral (motor) roots, and which penetrate the body and its appendages. The first enters the neck; the second and third join and enter the arm; the fourth to sixth penetrate the skin and muscles of the trunk; the seventh to ninth join by a plexus to form the sciatic nerve which supplies the leg, and the tenth enters the posterior portion of the body.

_Questions._

1. Which lobes of the brain are paired? Give at least two possible causes or reasons for their double structure.

2. The optic lobes are connected with the eyes. Compare their size with that of the other parts. Of how much use do you think they are to the frog?

3. If folds or convolutions in the surface of the cerebrum indicate intelligence, thoughtfulness, or mind, what do you infer as to the frog's mental condition and power to think?

4. Has the frog brain or "brains"? Explain.

5. Name several things done by an animal's brain.

6. Which of the spinal nerves are specially large? Why should they be large?

7. What advantages are there in the frog's having a dorsal nerve cord instead of a ventral one, as the earthworm has?

What would be the effect of cutting or breaking the dorsal root
of a spinal nerve? the ventral root? the entire spinal cord? How
do you explain the convulsions of the brainless (beheaded)
chicken or frog?

8. What kinds of impulses originate outside of the nerve center,
and what kinds in the center?

9. Sensations reach the cord and brain through the dorsal root of
the spinal nerve. What kinds of messages travel through the
ventral root, and in what direction do they go?

_Suggested drawings._

a. The brain.

b. The spinal cord and its nerves.

c. The nervous system.

d. A diagram of the cord and its nerves, showing the kinds and the directions of the nerve impulses.

The Endoskeleton of the Frog

_Materials._

Prepared frog skeletons mounted in glass-covered boxes or in other cases suitable for individual study; other vertebrate skeletons for reference.

_Observations._

The pupil should examine his specimen and identify the following structures:--

_A. Skull:--_

1. _Cranium_, or brain case, the central and hinder portion.

2. _Nasal bone_, a triangular bone lying in front of each large opening, or _eye orbit_, and attached to the anterior end of the cranium.

3. _Premaxillaries_, a pair of small bones which form the tip of the nose.

4. _Maxillary_, a slender bone forming the side of the upper jaw.

5. _Dentary_, the bone of the lower jaw, corresponding to the maxillary.

6. _Occipital foramen_, the posterior opening or entrance into the cranium, normally covered dorsally by cartilage and most easily seen in a separate skull.

_B. Vertebral Column:--_

1. _Cervical vertebra_, the first vertebra, supporting the skull.

2. _Dorso-lumbar vertebræ_, vertebræ with small lateral processes.

3. _Sacrum_, the ninth vertebra, bearing extra long lateral processes or "arms."

4. _Urostyle_, the last vertebra, lying in the median line, a long, slender, blade-like bone, really formed by the fusion of several vertebræ.

_C. Vertebra:--_

1. _Centrum_, the solid, nearly circular portion.

2. _Lateral process_, one of the paired projections, extending outward on either side.

3. _Neural spine_, the single projection, extending toward the dorsal side.

4. _Neural arch_, formed largely by a connection between the lateral process and the neural spine. The arch above and the centrum below inclose the _neural canal_.

_D. Pectoral, or Shoulder, Girdle:--_

1. _Sternum_, the "breastbone," extending along the median ventral line.

2. _Coracoid_, a heavy bone extending from the sternum sidewise to support the arm.

3. _Clavicle_, the "collar bone," a light bone in front of the coracoid.

4. _Scapula_, the "shoulder blade," a broad, thin bone which arches around to the dorsal side.

_E. Pelvic, or Hip, Girdle:--_

1. _Ilium_, a long, slender, curved bone, with its mate uniting to form an inverted "wishbone"; it is joined to the sacrum.

2. _Pelvis_, the region of the socket at the junction of the ilia.

_F. Fore Leg, or Arm:--_

1. _Humerus_, the single bone of the upper arm.

2. _Radius_, the bone of the lower arm on the thumb side; in the frog united to the ulna.

3. _Ulna_, the bone of the forearm opposite the radius.

4. _Carpals_, small bones of the wrist.

5. _Metacarpals_, a single series of long bones forming the palm of the hand.

6. _Phalanges_, the bones of the fingers and thumb (singular phalanx).

_G. Hind Leg:--_

1. _Femur_, the thigh bone, next to the body.

2. _Tibia_, the larger bone of the lower leg on the inner side; in the frog united to the fibula.

3. _Fibula_, the smaller bone of the lower leg.

4. _Tarsals_, the small bones of the instep.

5. _Metatarsals_, the long bones of the instep.

6. _Phalanges_, the bones of the toes.

_Questions._

1. Whereabouts in the frog has nature made an attempt to inclose delicate or vital structures in bony cases?

2. Examining the inside of the mouth, find the teeth. Judging from their size and structure, of what use are these teeth?

3. What advantages can you see in having the arms and legs attached to girdles instead of having them fastened directly to the vertebral column? How has their development affected the shape of the trunk, as opposed to that of the fish?

4. Make a comparison of the two girdles as to their attachment to the spine and their consequent rigidity or freedom of movement.

5. How many vertebræ are there in the spinal column? What advantage can you see in having the column composed of many small vertebræ instead of a few large ones? Enumerate those having a special form or structure, and state the use of each.

6. On the vertebræ notice any irregularities, prominences, or roughenings. For what are such bones better adapted than smooth bones would be?

7. How is the frog's humping permitted? How are the urostyle and the pelvis connected, if at all? Has this any effect on motion? (See living frog.)

8. In parallel columns, keeping corresponding parts in a line, tabulate the bones of the fore and hind limbs.

9. State how extra length has been attained in the hind leg, and give the purpose or the result of this lengthening.

10. In the forearm notice the fusing of the radius and ulna. How would these parts act in rotating the hand, as compared with your own, where they are free? Compare also the tibia and fibula. Where in the frog's leg is turning made possible by the use of parallel bones?

11. Compare the frog's hand and foot as to number of fingers and toes; as to length and spread. Have any fingers or toes only two phalanges?

12. How would an inner skeleton affect the growth and the size of an animal, as compared with an outer skeleton, like the clam's?

13. How would the lack of an outer skeleton influence sensitiveness, activity, and intelligence?

_Suggested drawings._

a. The skull and trunk, with appendages of one side.

b. Each set of bones separately, as the skull, the column, etc.

Comparative Study of Amphibia

_Materials._

Various amphibia, either dead or alive, such as newts, mud puppies (_necturus_), salamanders, and several species of frogs and toads, especially tree toads.

_Observations._

Answer the following questions with respect to each animal:--

1. What regions of the body are present? What is the general shape and size of the body?

2. For what kind of locomotion are the limbs fitted? How?

3. Have the hands and feet any special adaptations? If so, what are they and for what purpose?

4. With what organs does the animal breathe? If with gills, are they external or internal?

5. Judging from the specimen, what do you think is the habitat? Give reason for your answer.

Summary from the Comparative Study of Amphibia

1. Which of the amphibia in this study are fish-like in character? What are the fish-like characters? Do you think these fish-like amphibia are of a lower or higher type than the others? Give reasons for your answer.

2. Show how the variation in (a) the form of the body, (b) color patterns, and (c) the structure of the legs and arms of the amphibia are related to habitat and mode of life.

Amphibia: A General Review and Library Exercise

1. The usefulness of the American toad.

2. The breeding habits of the common frog; of the Surinam toad; of the obstetrical toad; of the "smith."

3. The development of the axolotl.

4. The habits of the tree frogs and their variable coloration.

5. The croaking of frogs and of toads.

6. The flying frog of Ceylon.

7. The distribution and habits of the hellbender; of the mud puppy; of the Congo "snake."

8. The general absence of the amphibia from arid regions.

9. Frog farming for city markets.

10. Protective devices of various amphibia.

11. Toads and warts.

12. The homing and water instincts of toads.

13. Hibernation, seasonal or prolonged, of toads and frogs.

14. The changes in the respiratory and circulatory system during metamorphosis.

15. Ontogeny and phylogeny, as illustrated by amphibia.

16. The structural defects which would prevent an ambitious frog from becoming a highly trained and skillful animal.

17. The classification of amphibia, with examples.

18. The kinds of frogs and toads found in the region where you live.

#C. STUDIES OF LIVING REPTILES#

#Showing Diversity of Adaptation among closely related Animals#

The Snake

1. What is the shape? What regions are present? How do you distinguish between the trunk and the tail? Has the tail any use? What are the advantages of a body without limbs?

2. Describe the snake's path in locomotion. How is locomotion accomplished? Is the absence of limbs a hindrance to the animal in its locomotory activity?

3. Describe the appearance and movements of the tongue. Of what use are these movements of the tongue?

4. What evidence is there that the snake breathes with lungs?

5. What sense organs do you find? Compare the ears and eyes with those of the frog. What explains the peculiar staring appearance of the eyes?

6. What is the color scheme? Does it appear to be protective? If so, how?

7. Of what does the exoskeleton consist? How are the scales arranged? What variations in the size of the scales do you find? What special use have some of the scales? How fitted for this? How does a snake moult? Appearance before and after moulting.

The Florida Lizard

1. Describe the body as to regions and shape. Is the tail of use?

2. What are the lizard's locomotory abilities? How is it fitted for living in trees?

3. Feed the lizard flies or meal worms and describe its method of capturing them.

4. Compare the lizard's respiration and sense organs with those of the snake and frog.

5. What is the usual color of the lizard? What have you discovered about its power to change colors? How may this be of use to it?

6. Of what does the exoskeleton consist? Is the entire body covered? How are the scales arranged? How does the lizard moult?

The Turtle

1. In what important ways does the body of the turtle differ from those of the snake and lizard?

2. What methods of locomotion has the turtle? For which method is it best fitted? How? Why are its movements in water so much less clumsy than on land? (Compare weight on land with weight in water.) Compare the efficiency of the locomotion of a turtle with that of a lizard and suggest a reason for the difference.

3. What do turtles eat while in the laboratory? Since turtles have no teeth, how can they bite off their food?

4. What can you discover with respect to the respiration of the turtle? Does it breathe when under water?

5. What sense organs has a turtle? Which appears to be most highly developed? How do you know?

6. In what various ways is the turtle protected against enemies? (You should state several.) Are you afraid of a turtle? If so, why? Why does the turtle need more protection than the snake or lizard?

7. Describe the color pattern of the turtle you are studying. Is this arrangement of colors the same for others of the same species?

8. Describe the arrangement of the epidermal plates of the turtle's shell. Are the arrangement, number, and form of plates the same for all turtles of this species? Compare with the plates of other species. What variations do you find?

Reptiles: A General Review and Library Exercise

1. Characteristics of reptiles.

2. Orders of reptiles. Characteristics and examples of each order.

3. Poisonous snakes found in the United States. The poison fangs of a rattlesnake. Habits of the rattlesnake.

4. Cures for snake bites, fabled and real.

5. Snake charming.

6. Famous poisonous snakes and their habits.

7. The characteristics and habits of alligators.

8. The characteristics and habits of marine turtles. How they differ from pond turtles.

9. For what is each of the following noted? Where does it live? The terrapins? the horned toad? the Gila monster? the chameleon? the glass snake?

10. Reptiles of former (geological) times compared with those of the present.

11. Care of eggs and young. Swallowing of young by snakes.

12. Food of snakes. Defend the proposition that non-poisonous snakes are beneficial and should not be killed wantonly.

13. Investigate and write an account of the economic value of reptiles.

#D. STUDIES OF BIRDS#

#Vertebrates specialized for Flight#

The Living Pigeon

_Materials._

Living pigeons in cages, and, if practicable, other birds such as chickens, canaries, and sparrows.

_The Body._

1. What divisions of the body are present? Compare the relative size of these divisions with that of other vertebrates studied. Can you account for the great increase in bulk of the trunk over the other divisions? How do you account for the longer neck?

_Flight._

2. What is the shape of the body? How is the body made smooth? To what is the shape and smoothness adapted? (Recall the appearance of a plucked pigeon or chicken.)

3. Observe the size of the wings by measuring their width and spread (measured from tip to tip when outspread). Where on the body are they attached? How is this point of attachment advantageous? What is the shape of the upper surface of a wing when spread? of the lower surface? How is this shape advantageous in flight?

4. Where are the largest and strongest feathers? How are they arranged with respect to each other: (a) to prevent air passing through on the down stroke of the wing? (b) to permit folding?

5. What is the shape and width of the tail when outspread? when folded? In what way does the tail assist in flight?

_Walking and Perching._

6. Identify the parts of the leg as in the frog. (See study of frog.) With what exoskeletal structures is each part covered? How many toes are there? Does the pigeon walk on its foot or on its toes? Where is the ankle joint?

7. The bird's legs are arranged to support the body. How is this brought about? Compare with the lizard and frog in this respect.

8. Explain how the legs are adapted (a) to preserve the balance of the body, and (b) for perching. Are they well or poorly adapted for locomotion? Explain. For what other purposes are the legs sometimes used?

_Feeding and Drinking._

9. What is the form and character of the jaws of the pigeon (called the beak)? Offer food, and watch the pigeons eat. How does a pigeon seize and swallow food? Does it chew the food? Locate the crop. If the pigeon chewed its food, would it have a crop? Why? How does a pigeon drink? How does the chicken drink?

_Respiration._

10. What parts move in breathing?

11. Compare roughly the body temperature (by touch) of man, the pigeon, and the frog. Which has the highest temperature? which the lowest? How can you account for the higher temperature of the bird? (Which of the three must be able to endure long-sustained effort? What is the effect on your own body of long-continued effort?)

_Sense Organs._

12. Identify the eyes, ears, and nostrils, and describe their location. What are the advantages in having the eardrum at the bottom of a canal? Is there any disadvantage? What is the probable function of the inner thin eyelid? How does it work?

13. Investigate the power of response of the special senses. Which seems to be the most alert? State the experiments which you used and your reasons for your answers to this question. Which senses are most serviceable in finding food? in protecting against enemies?

_Protection._

14. In what different ways are feathers protective to the bird? Study the arrangement of the feathers to find how protection is increased in this way. How do the feathers and parts of feathers which lie next the body differ from those which are on the outer surface? What parts of the body are unprotected by feathers? How are these protected, if at all?

15. Note the flexibility of the neck. Through what part of the arc of a circle can the pigeon turn its head? How is this especially important to birds?

16. What means of defense has the pigeon when attacked?

_Summary._

1. Make a list of the important adaptations of the pigeon, (a) to flight, (b) to feeding, (c) to perching, and (d) to protection.

2. Which is the most highly specialized, the fish, frog, snake, or bird? Give reasons for your answers.

3. In what various ways are feathers of use to the bird?

_Suggested drawings._

a. Side view of the head.

b. A foot.

c. A wing.

d. Side view of the pigeon.

Supplementary Studies of the Pigeon

These topics and questions should be answered from experience with pigeons and observations of their habits and behavior, and from books to be obtained from the school and public libraries.

1. The homing instinct of the common blue pigeon and of carrier pigeons.

2. Nesting habits, number of broods and number of young in each brood, feeding the young. Why is this method of feeding the young necessary?

3. Varieties or breeds of pigeons. How the various varieties were produced; how they are kept true; reversions of type.

4. Darwin's experiments with the pigeons; object of the experiment. Whitman's experiments.

The Exoskeleton of the Bird: Plumage

_Materials._

Living birds, as perhaps pigeons, or mounted or stuffed skins, separate feathers, portions of feathers, microscopes.

_Observations._

The pupils should study the arrangement of the feathers and their variations in form and size, and should identify the following principal kinds:--

_Contour feathers_, those feathers, generally broad, which cover the body, giving to it its outline and color.

_Coverts_, those feathers which cover joints, such as the joints of the wing and tail.

_Primaries_ or _pinions_, the long stiff feathers of the outside of the wing, used in sustaining the bird in flight.

_Secondaries_, the shorter, more symmetrical feathers lying next and over the primaries.

_Down_, soft feathers found on young birds and next to the skin on some adults.

_Thread feathers_, best seen about the eyes, ears, and beak.

_Quill_, the bare stiff portion, one end of which is inserted in the skin. Examine its internal structure.

_Vane_, the broad expanded portion, the part ordinarily seen on the bird.

_Shaft_, the mid-rib of the vane.

_Barbs_, the delicate outgrowths of the shaft making up the vane.

_Barbules_, the subdivisions of the barbs, some of which are provided with hooklets. These may well be studied microscopically.

_Questions._

1. How is the plumage arranged to offer least resistance to the air in flight? How does a bird sit when exposed to the wind?

2. In a column write the names of the parts of a feather, and opposite each part state its particular use.

3. Of what use are the hooklets on the barbules?