The Origin and Transformation of Animals. 97 



rous retain them for internal development ; but birds, worms, 

 reptiles, and men, all are hatched. 



The viviparous, and many of the oviparous tribes, resemble 

 their parents as soon as they have passed the foetal stage. The 

 marsupial animals, such as the kangaroo, forming no real 

 exception, as the seclusion of their young in the ,pouch is only a 

 second act of gestation. In other species — all of them oviparous 

 — the offspring, at the moment of leaving the egg, differs com- 

 pletely from both its father and its mother. It may possess 

 organs which they have not, and be destitute of organs with 

 which they are furnished, so that changes and metamorphoses 

 are required to bring it back to the original type. M. Quatre- 

 fages proposes to restrict the term transformation to the desig- 

 nation of those changes which the germ experiences in becoming 

 an embryo, or which it undergoes while still enclosed in the egg. 

 Metamorphosis, in like manner, designates changes altering the 

 character of the creature, and, occurring after it has left the egg, 

 or been hatched. Geneagenisis refers to the changes which 

 1 c affect the generations themselves." 



In discussing the transformations of the egg, M. Quatrefages 

 refers particularly to his own observations of the Serpula and 

 Teredo. After the laying of their ova, the eggs, whether fecun- 

 dated or not, exhibit an internal commotion ; " a mysterious 

 force agitates the yolk ; granulations accumulate now at one 

 point and now at another," so that the shadowy mass changes 

 its aspect every moment. M. Quatrefages considers that simi- 

 lar changes take place in the eggs of higher animals although 

 they may be slower, and more difficult to trace. In the Serpula 

 and Teredo eggs the agitation causes the " Purkinje vesicle" 

 and the " spot of Wagner" — to disappear. If the eggs have not 

 been fecundated, the movements become accelerated and irre- 

 gular, and, finally, decomposition ensues. All through the 

 animal kingdom the male element appears to excite and regu- 

 late the germinating force. In the eggs of the creatures named, 

 a little nipple appears on the surface of the altered yolk, from 

 which one or two transparent globules are expelled, the use of 

 which is unknown. 



This occurs whether the eggs have been fertilized or not. 

 If fertilized, the expulsion of the globules is succeeded, " whe- 

 ther it be in the mammalia or the serpulge," by a short period 

 of repose. When activity recommences constrictions become 

 visible, and the yolk assumes a mulberry aspect. The details of 

 the process varyin different animals, "but in all, the consequence 

 of the phenomenon is the formation of a primitive organized 

 layer which envelopes the yolk, and is called the blastoderm. ■ 

 As soon as organization begins, it assumes distinctive characters ; 

 " the germ becomes the embryo, and from its origin reveals the 



