STUDY OF FISHES 



141 



its stroke tends to bring the head downwards, towards the floor 



of the sea. The unsymmetrical tail is usually associated with a 



ventral (not terminal) 



mouth, and with the 



habit of feeding at the 



bottom. 



(e) In connection 

 with the mouth (i) 

 The wide gape in many 

 cases, reaching an ex- 

 treme in the angler 

 Lophius piscatorius. 

 (2) The position of the 

 mouth, usually ter- 

 minal, but ventral in 

 the gristly fishes (skate, 

 shark, etc.) and in the 

 sturgeon. (3) The varied 

 assortment of teeth, 

 making a pavement 

 over the jaw in the 

 skate, hinged at the 

 base in the angler so 

 that they bend inwards 

 very readily, unequal in Fia 49> __ The dorsal surfac " e O f a skate- 



and Sharpness in illustrating the study of external characters. Very 



remarkable is the flat shape of the body and the 

 involved enormous extension of the pectoral fins (PC), 

 which are in this case the organs of locomotion. The 

 pelvic fins (PV) are relatively small ; the males are 

 marked by an extra piece (M). In correlation with 

 the flat body, which one may think of as flattened from 

 above downwards, there is a reduction of the unpaired 

 fins to a minimum at the end of the tail (CF). The 

 skull is prolonged in front into a snout, which is greatly 

 exaggerated in the saw-fish Pristis^ and the pectoral 

 fin is connected in a remarkable fashion with the sides 

 of the head. Behind the lidless eyes (E) there are the 

 spiracles (SP) by which water enters, passing out by 

 the other gill-clefts which lie on the ventral surface. A 

 few large skin-teeth or placoid scales are shown. The 

 mouth, the nostrils, etc. are on the ventral surface. 



CF 



the catfish, very sharp 

 in the eel, absent in the 

 sturgeon, and so on. In 

 a fish like the haddock, 

 note the teeth on the 

 roof of the mouth and 

 still farther back on the 

 wall of the pharynx. 

 (4) The frequent pres- 

 ence of a white tongue, 

 which does not con- 

 tain any muscle, which 



