10 ELEMENTS OF COMPARATIVE ZOOLOGY. 



fins are the pectorals; the posterior are the pelvic or ven- 

 tral fins. 



INTEGUMENT. On the trunk and tail are scales. Are 

 they regularly arranged ? Are there scales on the head ? 

 Do they extend on the fins ? Is there any skin over the 

 scales ? Is there skin on the head ? Can you trace the 

 skin of the head into the mouth ? Find dark pigment 

 spots on the body. Does the color belong to the scale or to 

 what ? Settle by pulling out a scale. 



Notice the lateral line running along a row of scales on 

 either side of the body. Does it continue on the head ? 

 Examine the scales with a hand-lens and see what causes 

 the line. Examine any scale with the hand-lens. Is it 

 margin regularly rounded (cycloid), or is it toothed or spiny 

 behind (ctenoid) ? 



THE HEAD. How many eyes are there ? Where are 

 they placed ? Are they movable ? Are eyelids present ? 

 Notice in each eye the colored iris around the central 

 black pupil. 



What is the position of the mouth ? See that it has a 

 bony framework, the upper jaw being composed of a pre- 

 maxillary in front, and behind this a maxillary which 

 when the mouth is open slides over the dentary or lower 

 jaw. Do any of these bones bear teeth ? Open the mouth 

 and examine the tongue. How much can it move ? Can 

 you find teeth anywhere inside of the mouth ? Feel with 

 a pin. 



How many nostrils, and where . situated ? Probe with a 

 bristle. Do they communicate with the mouth ? Can you 

 find any ears ? 



THE BRANCHIAL APPARATUS. Find the gill-opening, 

 a crescentic slit on the side bounding the head behind. In 

 front of it is the gill-cover or operculum, which may be 



