408 



accessory part of the vitellus ; and so we see it is wanting 

 sometimes, arises in different ways, presents very various 

 relations with the protoplasm, and behaves itself very diffe- 

 rently in the course of the first embryonic phenomena, 

 according to the particular case. 



Formation. — Sometimes it takes birth in the interior itself 

 of the protoplasm, and is elaborated by the cell-egg itself; at 

 other times it is formed by certain special cells, either in a 

 particular gland (deutoplasmogen of Van Beneden — vitello- 

 genous gland of previous authors), or in the same gland 

 in which the germs are formed, but in a special part of this 

 organ . 



Relations to the Protoplasm of the Cell-egg. — Sometimes it 

 is found in the ripe egg, in suspension in the protoplasm ; 

 sometimes it does not get mixed up with it. In certain cases 

 it is formed of well-marked cells ; more often it is composed 

 of drops or of refringent granules, or even of vesicular 

 elements, which have nothing in common with true cells. 



Role in Developtnent. — AVe have now seen that the deuto- 

 plasm behaves very variously during the first embryonic 

 phenomena; but its function is always the same. It plays a 

 ]nircly passive part ; it serves to nourish the blastoderm and 

 the embryo, and to furnish, by the combustion of the elements 

 of -which it consists, the force necessary for the production of 

 all the elements of the embryo, and for the accomplishment 

 of all the phenomena of foetal life. This deutoplasm, Avhich 

 is sometimes wanting, can be formed of distinct cells, and take 

 origin in a special organ ; and although it makes a part of 

 the egg, it cannot be regarded as an integral part of the cell- 



^3U' . . . • . 



It follows from this that the jiroposition generally admitted, 



" every egg is a cell,'^ has not that stamp of exactitude wliich 



should characterise any principle of science. 



But in every egg there exists a cell-egg, a germ which is the 

 first cell of the embryo. 



Side by side with this cell there exists in the q^^ a mass of 

 nutritive matters, possibly mixed with the protoplasm of the 

 cell-egg, and formed in its interior, as is seen in many verte- 

 brate animals. In that case, we may embrace it in the cell, 

 and say, with Schwann, that the egg is a cell as far as Verte- 

 brates are concerned. 



But when the deutoplasm is found outside the cell-egg, it 

 cannot be considered as forming an integral part of the germ, 

 and itself may be composed of cells, of which Ave have ex- 

 amples in many lower animals, which arc remarkable for 



