150 VERTEBRATES 



Back of the pectoral fins on the ventral side find a second 

 pair, the ventral fins. Examine them and compare with the 

 pectoral fins.-- Are they separated or attached on the ven- 

 tral side? 



Compare these two pairs of fins to the upper and lower 

 limbs of a person. Back of the ventral fins is found the anai 

 fin. Study it and compare it with the others. With refer- 

 ence to the right and left sides, where is it? 



Do you find a fin on the dorsal side? Note its shape and 

 position. It is the dorsal -fin. Is it made of hard or soft 

 spines? Are the rays segmented? How is it attached to 

 the body? On the posterior end of the fish, find the caudal 

 fin. Note its structure and compare it with the others. 

 How is it attached to the body ? What motions has it ? Are 

 the lobes equal or unequal? 



(3) Examine the covering of the body. Is it like any 

 covering yet studied? Take out one of the scales, examine 

 it where it was attached, and examine the skin at the point 

 where it was removed. Does it look anything like the scales 

 on the wing of the butterfly ? Note the shape and size of the 

 scales at the different parts of the body. Do the fins and head 

 have scales ? Scrape carefully both sides of a scale and place 

 it under the low power of the microscope. What is its struc- 



' ture? Has it grown out from the body like a feather? Do 

 you think it has had a rapid growth ? Make a drawing of a 

 scale (Xio). If the scale is round it is called cycloid, if 

 it is toothed it is ctenoid. 



(4) Do you notice spots of coloring in different parts 

 of the body? Is the coloring on the outer parts of the scales 

 or on the skin under the scales? These spots are pigment 

 cells and are simply bundles of coloring matter. Can you 



