Natural History of the Shark, 357 



would have been arranged in vain, and that Almighty Being, 

 who, by enabling us to foresee the physical wants that are to 

 arise, has enabled us to provide for them, would have left the 

 creatures for whom He has been so bounteously provident, to 

 perish, ignorant and irresolute, amid elements that seemed waiting 

 to obey them, and victims of confusion in the very midst of all 

 the harmonies of the universe *." 



We now proceed to consider the special oeconoray of Cartila- 

 ginous Fishes. 



In the Osseous Fishes the ova escape into the interior of the 

 ovary, and are expelled through an excretory orifice resembling 

 the duct of an ordinary gland. In the Cartilaginous Fishes, and 

 in all other Vertebrata, the germs burst from the exterior of the 

 ovarium, from whence they are generally conveyed as eggs out 

 of the body through intermediate tubes, or hatched internally ; 

 the oflFspring being retained within the body, to be nourished in 

 receptacles provided for the purpose, until they arrive at a con- 

 siderably advanced state of development. 



It is only by degrees that perfect ovigerous organs make their 

 appearance in Cartilaginous Fishes. In the Lamprey is found the 

 first appearance of the ovary common to the higher Vertebrata. 

 As there is no excretory duct, naturalists were long at a loss to 

 explain how the ova were expelled ; it is now ascertained that as 

 the eggs become mature they break loose from the nidus in 

 which they were generated, and penetrate into the peritoneal 

 cavity, and floating loose in the abdomen escape into the sur- 

 rounding water in countless numbers, by two orifices placed on 

 each side of the anal opening. 



Such is the first step in the provision for ovigerous organs in 

 Cartilaginous Fishes. 



In the Sharks and Rays it advances a step further, and the 

 female sexual apparatus receives the important addition of an 

 oviduct. In this passage the germ is seized on its escape from 

 the ovarium, and furnished with additional coverings necessary 

 for the security of the foetus. 



Some of the Rays and the Sharks are oviparous, and others 

 viviparous. To accommodate the species of each respectively to 

 their different circumstances, a different provision for the foetal 

 life is severally made. The means employed for attaining the 

 oviparous end are simple and beautiful. "About the middle of 

 the oviduct of the female, there is a thick glandular mass, des- 

 tined to secrete a horny shell in which the yolk and white of the 

 egg become encased." This coincides with the provision in birds 

 for investing the egg with a calcified covering, in other words, with 



* Moral Philosophy, Lecture VI. Physical Inquiry. 



