XV. THE DOGFISH. 

 (Scyllium canicula.) 



1. Form and Mode of Life. In the dogfish we have a 

 strictly aquatic type of vertebrate, a member of an order 

 of fishes found only in the sea. Like all the more highly 

 organized marine animals, it is carnivorous, and it is not at 

 all restricted in its diet, caring only for quantity. It is 

 really a small shark, differing from other sharks in little 

 save size ; and its structure differs in many respects from 

 that of the more familiar bony fishes, such as cod, salmon, 

 herring, or perch. 



The general build of the body is eminently adapted to 

 an aquatic life. The whole body is laterally compressed, 



^.^^..^^^isss^^^^^^^Sl^^^?*^ 



j^iiii^r??:;^^ 



Fig. S7. THE DOGFISH (Scyllium canicula, after Day's Britif.lt Fishes). 



and smooth in outline. Head passes into trunk and trunk 

 into tail without any sudden change. The tail is about 

 as long as the trunk, and tapers gradually behind, finally 

 curving upwards, the outline of the end being formed 

 by an unequally-lobed caudal Jin. Two median dorsal Jms 

 project from the back, and there is also a median ventral 

 (or anal) fin. Farther forward ventral ly, in the position 

 where the limbs would be found in a land-vertebrate, we 

 find paired fins, pectoral and pelvic. Though obviously 

 answering to limbs, these have none of the complex articu- 

 lations we have previously met : they are simply flexible 

 flattened expansions, and instead of directly performing 

 locomotion merely co-operate with the median fins in 



169 



