3 20 ZOOLOGY. 



Note other smaller nerves and cut these. How many are there? From 

 what part of the brain do the majority of them arise? Do the optic 

 nerves join at the point where they enter the brain? 



7. Skeleton. Pick the bulk of the flesh from the bones of an un- 

 injured skeleton. A few minutes of boiling or two or three days of 

 soaking in water will be of advantage in the final stages of cleaning. 

 Identify the axial skeleton and the appendicular. Do the appendages unite 

 directly with the axial skeleton ? Count the vertebrae. To what extent 

 do they differ? Can they be grouped into regions? Select a typical one, 

 and draw from various positions to show structure. Do any bear ribs? 

 Describe the posterior bone in the series. Identify the parts of the an- 

 terior and posterior limbs and girdles by referring to Fig. 159, and see to 

 what extent they depart from the type described there. Make outline 

 sketches of all the bones of the right girdles and appendages. What is 

 the nature and action of the various joints of the limbs? In the skull 

 notice how small a portion is brain-case. How is the great width of the 

 head secured? How is the lower jaw related to the skull? Make a sketch 

 showing the proportions of these various parts. In what position are 

 teeth borne? Examine the sternum or breast bone. How related to the 

 girdle? Of what parts is it composed? How much of it is cartilaginous? 



8. Development. Eggs of frogs and toads may be found in the early 

 spring in ponds or sluggish streams, floating or attached to submerged 

 objects. They occur in slimy strings or masses, each egg enveloped in a 

 jelly-like covering. Transfer these to the laboratory, and keep covered 

 with water in a shallow vessel. Change the water frequently, and keep 

 a close watch on the changes which they undergo. After hatching keep 

 water plants in vessels for the tadpoles to eat. 



Note appearance of the egg (with low power of microscope). 

 Gelatine; outer layer, not really a part of the egg. 

 Fertilized ovum ; the darker interior sphere, of protoplasm and yolk. 



If the eggs are recently laid, the beginning of segmentation will furnish 

 an interesting demonstration for the class. How are the first cleavage 

 planes related to each other? 



If more advanced, note especially : the gradual elongation of the 

 embryo, the enlargement of the head, development of the tail, hatching, 

 the external gills. What becomes of the gills? Do you find any trace 

 of mouth, eyes, nasal openings? Where do the legs first appear? What 

 becomes of the tail? Prove. Tadpoles of all ages may usually be found 

 in the shallow ponds. These should be compared with those reared 

 in the laboratory. Dissect one of the larger tadpoles, and examine 

 particularly the intestine and the gill chamber. 



335. Compare with the frog any other Amphibian types which can be 

 found, as the toad, the newt, or the salamander. Note especially the 

 differences in habits, haunts, external form, appendages, method and time 

 of depositing eggs, the form of the tadpoles, etc. 



