VEGETABLE AND ANIMAL OVULES COMPARED. 147 



which thus becomes divided into two cells. Very soon 

 each of these cells is divided into two others, which again 

 prove the same segmentation ; the mass of cellular tissue 

 thus formed, goes on developing, and ultimately organizes 

 itself into a seed which contains an embryo capable of repro- 

 ducing the plant. 



Now what relation subsists between the ovule of flower- 

 ing plants and the ovule of animals ? This is an interesting 

 question, deserving of some attention. In the higher order 

 of animals the ovule exists in the ovarian mass, or in tubes 

 which supply its place in animals of a simpler organization. 

 It appears at first under the form of a simple utricle, in the 

 inside walls of which exists another much smaller, called 

 the germinal vesicle. This last disappears after fecunda- 

 tion. It is within the primitive utricle that the vitellus 

 exists, a matter formed at first of a granular substance, 

 which, by.successive segmentation, divides itself into globules 

 more and more numerous. This body, the vitellus, by 

 degrees organizes itself into a tissue, the basis and frame- 

 work of the germ or embryo. The animal ovule is there- 

 fore represented in the plant by the embryonic vesicle, and 

 the granular matter which it contains is analogous to the 

 vitellus of the egg ; since both are transformed by successive 

 segmentations into cellular tissue, and finally into the em- 

 bryo. The embryonic sac and the walls of nucleus are only 

 the accessory parts, analogous to the yolk of the egg in 

 birds ; that is to say, they furnish to the young embryo the 

 first materials of nutrition, and end by being totally ab- 

 sorbed. 



Among vertebrated animals the development of the em- 

 bryo may be best observed in the eggs of fishes. Being 

 transparent, they do not require to be cut open, and by 

 sufficient caution the whole series of changes may be ob- 



