3S0 FISHES 



such the internal tunic of the general membrane ; but this amnios 

 embraces the A-itelkus as well as the foetus. 



The vitelliis has two tunics, both complete, nnd very fine. The 

 external is continued by its external lamina with the skin, and by its 

 interior with the peritoneum ; the internal, very vascular, is continued 

 with the membra nes of the intestines and their peritoneal tunic; the 

 cavity opens directly and visil.ly into that of the intestines, and the 

 yolky matter there flows. Tliere are some genera, as the squalus, in 

 which I have seen a lobe of interior vitellus always enclosed in the 

 abdomen of the foetus ; it is the same as an appendix of the intestine. 

 The arteries of this internal tunic come from the coeliac artery ; its 

 veins terminate at the vena portae. 



What distinguishes essentially the eggs of fishes, as well as those 

 of the batrachiansfroLH the eggs of animals which, once hatched, respire 

 always by the lungs, is the entire absence of the allantois and the um- 

 bilical vessels, wliich do not appear to show themselves at any period. 

 There is, consequently, no jjlacenta, and which are the vitellus. which is 

 always verymuch reduced in those foetuses of the shark ready to be born, 

 appears to me to adhere to the womb almost as fixedly as to a pla- 

 centa. Its cord is bristled with a quantity of vascular ramifications, 

 or of a species of long hair, very similar to that of the roots of trees. 



Most frequently the abdomen is not swelled even by that interior 

 lobe of which we have just spoken ; but sometimes, as in the ana- 

 bleps, the vitellus has already disappeared to a considerable extent 

 externally, whilst the abdomen has still a swelling formed by a dilata- 

 tion of the skin of the fish, and in the interior of which mav be seen, 

 with the intestines, the remnant of the pedicle of the viteUus. This 

 swelling, which already shows small scales scattered up and down 

 vipon it, contract by degrees, and then the scales approach each other. 



In whatever manner the fish has been brought into external life, it 

 is, from that moment committed to itself, and with the sole responsi- 

 bility of providing for its wants. The greatest number of them 

 perish, devoured by larger fishes, aquatic birds, or reptiles; those 

 which survive, assume a growth more or less rapid according to their 

 species : in certain fishes this growth continues almost the whole of 

 their lives, and the life of some is very long. It is pretended that 

 that of the carp has been known to be more than a century ; but this 

 long life, which is attributed to the slight hardness of the bones, is 

 far from being granted to all the species. 



CHAPTER IX. 



General Recapitulation of the Organization of Fishes. 



Such is the general idea, according to our view, of the nature and 

 organization of fishes, an idea which will not be complete until we 

 add a particular description of each of the species, in stating every 

 thing that is peculiar to each. 



The general result then, according to us. from the whole of these 

 observ'ations on their peculiar organizations, is, that fishes constitute 



