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Chapter XII 



THE DOG-FISH. Scyllium canicula. 



The dog-fish, together with the sharks and skates, belongs 

 to the group of fish known as Elasmobranchs, the great 

 majority of which are powerful swimmers, of carnivorous 

 habits, and exceedingly voracious. One of the chief characters 

 of the group is that almost the whole of the internal skeleton 

 remains cartilaginous throughout life : hence Elasmobranchs 

 are frequently spoken of as cartilaginous fish. 



There are several kinds of dog-fish found off our own 

 coasts. The following description is taken from one of the 

 most abundant species, but will apply with but slight changes 

 to any of the common forms. Skates differ markedly from 

 dog-fish in external appearance, owing to the enormous size 

 of their pectoral fins, which form the great lateral wing-like 

 expansions of the body ; as regards internal structure, how- 

 ever, the differences are comparatively unimportant, and a 

 skate might easily be dissected by following the directions 

 given in this chapter. All the measurements here given are 

 taken from a dog-fish of about two feet in length, which will 

 be found the most convenient size for dissection. 



Scyllium canicula, like most other species of dog-fish, lays 

 eggs, which are of large size, and enclosed in horny capsules 

 produced at their angles into long spirally twisted strings 

 for attachment. In many cases the eggs are retained within 

 the oviduct during part or the whole of their development ; 

 and in some few species a still closer relation is established 

 between the mother and the embryo, similar in many respects 

 to the placenta of mammals, whereby the embryo obtains 



