CHAPTER III. 



OP GEOWTH IN THE ANIMAL KINGDOM. 



When motecnlaxly the male fecimdatiKg substance has blended 

 with that of the female oyrikDii (Fig. 40), has impregnated it, the 

 work of evolution, that iato say, of generation and multiplication of 

 the anatomical elements, has commenced 

 in that ovulum. Growth commences 

 in the ovulum by the inferior process 

 of segmentation or fracticmment (Fig. 

 41). Cells, all like each other, juxta- 

 pose themselves to form a membrane, 

 in a point of which appears the rudi- 

 ment of the embryon. The primitive 

 membrane is the blastoderm ; the first 

 indication of the embryon is called 

 the embryonary spot. In this point the 

 blastodermic membrane is double ; it 

 is composed of an external vestment, 

 serous or animal; and of an internal 

 vestment, mucoiis or vegetative. From 

 the first vestment specially proceed, 

 in the vertebrates, the teguments and the organs of the life 

 of relation ; the second vestment gives, above all, birth to the 

 apparatus of vegetative life. These first phenomena of develop- 

 ment are perceptibly the same in the whole animal kingdom, 

 from the lowest point to the highest. 



Fig. 40. 



An ovum of mamniifer (a simple 

 cell) : a, nucleole {%udeohts) or 

 germinative point of the ovum ; 

 6, wwclenis, or germinative vesicle 

 of the ovum ; c, cellular sub- 

 stance or protoplasm, yolk of 

 ovum ; d, enveloping mem- 

 brane of the yolk in the mam- 

 mifers ; it is called Mmibrama . 

 pelhuMa, on account of its trans- 

 parency. 



