264 ELEMENTARY ZOOLOGY 



the body is thickly covered with firm, hard scales, arranged 

 like the shingles on a roof. Remove one of these scales 

 and examine it under a hand lens. What sort of an edge 

 has it ? Such a scale is said to be ctenoid. 



The body of the sunfish terminates behind in the 

 caudal fin, a series of cartilaginous rays connected by thin 

 skin and attached to a bony plate at the end of the back- 

 bone. Along the median dorsal line will be noted another 

 fin composed anteriorly of spines and posteriorly of soft 

 rays jointed and branched. This is the dorsal fin. How 

 many spines has it ? Anterior to the caudal fin on the 

 ventral surface is a median unpaired anal fin. How many 

 spines has it ? Anterior to the anal fin are the ventral 

 fins, while on the sides of the body back of the head in 

 a line with the mouth are found the pectoral fins. The 

 ventral fins, attached to a rudimentary pelvis, correspond 

 to the hind legs of the other vertebrates. The pectoral 

 fins, attached to the shoulder girdle, correspond to the 

 arms. In front of the anal fin note a small pit-like open- 

 ing, the opening from the kidneys and reproductive organs, 

 and just anterior to this a large aperture, the amis. At the 

 anterior end of the head note the broad moutli, surrounded 

 by a complicated system of bones. Note the large eyes 

 surrounded by a series of small bones, the orbital chain. 

 Just anterior to the eyes are two pairs of openings, one 

 pair of each side opening into a closed sac. What are 

 these openings ? Note the presence of various bones on 

 the side of the head, each covered with a thin layer of 

 skin. These are membrane bones, characteristic of fishes. 

 Are there any external ears in the fish ? Examine the in- 

 side of the mouth. Is there a tongue f If so, of what char- 

 acter ? Are there teeth f If so, where are they situated ? 



Note along each side extending to the base of the tail 

 a line of modified scales, on each scale a little mucous 

 tube, the whole series constituting the lateral line. These 



