96 ELEMENTS OF COMPARATIVE ZOOLOGY. 



the large sciatic nerve. Trace the nerve backwards towards 

 the trunk. Does it pass through any bones ? Trace the 

 nerve inside the dorsal wall of the body-cavity. Do you 

 find a plexus like that of the fore limb ? If so, how many 

 nerves enter into its formation ? 



COMPABISONS. 



With three columns, for Ichthyopsida, Sauropsida, and 

 Bat respectively, answer the following questions : 



(1) Is hair present ? 



(2) Do you find true scales or feathers ? 



(3) Is there an external ear ? 



(4) Do you find anything like gill-slits? 



(5) How many chambers in the heart ? 



(6) How many aortic arches ? 



(7) Do the aortic arches bend to the right or to the left ? 



(8) Is a diaphragm present ? 



(9) Do they produce eggs ? 



