FISHES. 379 



which passes through the gland. The egg of the chimceras is also 

 enveloped in a strong shell wliich is flat, horny, oval, and velvetty. 



To all these shells of the chondropterygians, which are of a horny 

 nature, and not heing lialjlc to break like those of the eggs of birds, 

 nature has given an opening at one of their ends, from which the 

 young may remove the edges and get out when it has acquired a suf- 

 ficient development; it has even been thought that when the eggs 

 are layed, tliis opening allows the water to aid in the respiration 

 of the" foetus; but I have always found it closed by a naembrane*. 



In the viviparous squalus, whose young is hatched in an oviduct 

 or in the womb, such as the sharks, there is only a membi-anouS 

 envelope round the foetus, in which is always recognized the tor- 

 tuous cords of the eggs of other species. 



Certain species carry their eggs upon them during some time after 

 having layed them, and even some until they are hatched. Thus the 

 syngatlmes have, behind the anus under the tail, a hole shut by two 

 scaly pieces, as by two lids, in which tlie eggs are deposited seriatim, 

 and where they remain until the young are hatchedf . The aspredes 

 carry them suspended to the skin of their belly. 



But the greatest number of fishes scatter their eggs in the water, 

 agglutinated by a mucilage which enveloped them and attaches 

 them to stones, or aquatic plants, sometimes in grovips, sometimes in 

 strings or in net-work according to their species. These eggs are 

 transparent globules, in the middle of which is seen the yolk. In 

 this state the male fecundates them by distributing the milt, and it is 

 in this distribution or fecundation of their eggs, that the fishes 

 exhibit the greatest activity : it is then that many come up the rivers, 

 that others travel in troops, and that others follow or pursue each 

 other, either in pairs, or in a much greater number. 



The germ shows itself with more or less rapidity in the fecundated 

 egg, according as both the temperature, and the growth in general are 

 tardy : the young generally comes out before it is very large, by 

 piercing the envelope with its tail|. 



In viviparous osseous fishes, such as the silures, the anableps, certain 

 blenuies, &c., the egg grows even in the ovary, as much as is neces- 

 sary for the foetus, which is there developed ; and there are species 

 in which it becomes remarkably large. The young having been 

 completely hatched, breaks the egg and the membrane which had 

 retained it. 



All these eggs are composed, besides the foetus, of a vitellus which 

 commrmicates by a pedicle with the intestine of the foetus, and 

 which diminishes, in proportion as the foetus grows, and of an external 

 membrane, which corresponds to the membrane of the egg-shell of 

 birds, and which contains the foetus and its vitellus. 



I have not hitherto detected an amnios, at least unless we regard as 



* See Home, Lessons of Comparative Anatomy, Lesson Thirtieth. 



t It is this improper view which made Aristotle say (Hist. An., t. vi. p. 15), 

 that the eel (le syngnathe) is ruptured when the time of laying approaches, and 

 that it has under the belly a rleft which closes after laying, &c. 



+ On the fecundity of the eggs of fishes, see Carolini's Treatise of the Generation 

 of Fishes and Crabs (in Italian, Naples, 1787, and 1784, in 4to. ; in German, 

 Berlin, 1792, in 8vo.) 



