64 M. Balbiani on the Reproduction 



this point of the cells composing it; and the internal granular mass 

 projects through this orifice. We then clearly perceive, either 

 directly or by means of reagents, that the whole inner surface of 

 the blastoderm is lined with a delicate membrane which extends 

 like an envelope round the central vitelline mass. 



It is this membrane, with a portion of its contents, that pro- 

 jects, as just stated, through the orifice at the posterior extre- 

 mity of the blastoderm. This hernial portion attaches itself to 

 the corresponding epithelial cells of the ovarian chamber, which 

 are hypertrophied, and becomes as it were engrafted upon them. 

 When this connexion is established, the vitellme vesicle becomes 

 constricted in the interior of the cavity of the blastoderm like a 

 cell in process of division, and then separates into two juxta- 

 posed secondary cells, — the posterior adherent to the epithelium 

 of the chamber, the other, or anterior, being completely free in 

 the above-mentioned cavity. I have sometimes succeeded in 

 detecting a very pale granular nucleus in the posterior vesicle, 

 and less distinctly in the anterior one ; they, therefore, present 

 all the characters of true cells. These vesicles or cells are to be 

 the origin of the male and female generative elements of the 

 future animal — that is to say, of the ova on the one hand, and 

 the spermatic cells on the other. In fact, by a phenomenon of 

 germination which I cannot describe here in detail, each of them 

 becomes covered at its surface by a generation of small cells, 

 which, when once produced, increase in size and continue to 

 multiply on their own account. From this results the forma- 

 tion of two very distinct cellular groups placed side by side in 

 the cavity of the blastoderm. The group produced by the 

 herniated vesicle engrafted upon the exterior epithelium repre- 

 sents the male element, and will give origin to the fecundating 

 corpuscles ; that which originates from the free vesicle in the 

 interior of the ovum is, on the contrary, formed by the totality 

 of the female elements — that is to say, the generative cells of the 

 future ovules, surrounded by their nutritive cells. This latter 

 group soon subdivides into a certain number of secondary groups, 

 corresponding with that of the ovarian sheaths which are sub- 

 sequently to be formed. The cells which compose it remain 

 always transparent and colourless, and are also smaller than 

 those of the first group, the cells of which, on the other hand, 

 are soon permeated by numerous small green or yellow granula- 

 tions, which enable them to be recognized with the greatest 

 facility*. The generative vesicles of the two sexual masses be- 



extremity which is directed towards the external sexual orifice, and that of 

 anterior pole to that which looks towards the terminal chamber of the 

 ovarian sheath. 



* This yellow or green mass, which is met with in most Aphides at all 



