488 



SQUALID^. 



fins and other parts, furnish characters by which the different 

 divisions forming this family are distinguished. Among the 

 Sharks, the males differ from the females externally in having 

 an elongated cylindrical appendage at the inner edge of each 

 ventral fin, the uses of which are not understood. The third 

 species of Shark here figured represents a male fish, and 

 shows the peculiarity of the ventral fins in that sex. The 

 females are not furnished with these appendages : the figures 

 of the first two species represent females, and the vignettes 

 to each show on an enlarged scale the specific and sexual 

 peculiarities of the ventral fins, and also the difference in the 

 form of the mouth in these two species. 



Of the true Sharks, some produce their young alive, and 

 are called viviparous ; others, like those under present consi- 

 deration, bring forth their young enclosed in horny cases, 

 an example of which is here introduced, a portion of one side 

 of the case being removed to show the young fish within. 



On examining adult females, the ova are observed in differ- 

 ent stages of growth descending from the ovaries, usually in 

 pairs, frequently one in each oviduct, becoming enclosed in 

 the protecting covering when about to be excluded. These 

 cases, which are frequently found on the sea-shore, and are 

 called Mermaid's purses, sailor's purses, sea purses, &c. are 



