362 Prof. E. Claparede on the Reproduction of the Aphides. 



commence their evolution even in the interior of the embryo 

 still contained in the body of its mother ; consequently there is 

 neither alternate generation nor parthenogenesis. 



The two cellular masses to which M. Balbiani ascribes so 

 important a part in the reproduction of the Aphides really existj, 

 as we may easily ascertain. M. Mecznikow has studied them 

 with extreme care. The colourless one he regards as a blasto- 

 gene or pseudovarium, so that he attributes to it the same phy- 

 siological part as M. Balbiani. But the other, the green mass, the 

 testicle according to M. Balbiani, is regarded in a very different 

 light by M. Mecznikow ; he gives it the name of secondary 

 vitellus, because he considers it a magazine of material fitted to be 

 assimilated in the course of the organogenetic process. We 

 shall see that this latter interpretation is by far the most pro- 

 bable; but for this purpose it is necessary to go back to the 

 origin of the matter. 



The extremity of each compartment of the pseudovarium is 

 occupied by numerous nuclei disseminated in a protoplasm. 

 These nuclei are the germinal vesicles of the future ovules ; in 

 fact the lowest one becomes isolated from the others, and sur- 

 rounds itself with a mass of protoplasm, in w^hich refringcut 

 granules soon make their appearance : this is the ovule. M. 

 Balbiani, adopting throughout his memoir M. llobin^s theory 

 of the production of cells by gemmation upon the periphery 

 of a blastoderm, represents the ovules as originating by gem- 

 mation upon the surface of a central cell. M. Mecznikow no- 

 where mentions or figures this central cell of the pseudovarium, 

 nor have I succeeded in discovering it. But, however this may 

 be, as soon as a pseudovum attains maturity in the lower part of 

 the compartment of the pseudovarium its evolution commences. 

 We soon see, in the midst of the vitelline granules, several 

 clear nuclei, very similar to what the germinal vesicle was 

 originally. M. Mecznikow regards these nuclei as having been 

 produced by the division of this germinal vesicle. Is he quite 

 right upon this point ? I cannot venture to decide*. What is 

 certain is, that these nuclei multiply and advance to the peri- 

 phery, where they are found lodged in a layer of protoplasm, 

 constituting thenceforward a true blastoderm. This membrane, 

 in fact, becomes cellular by a differentiation of the protoplasm, 

 which groups itself in little masses round each of the nuclei. 



M. Balbiani, indeed, represents matters in a very different 

 light; but it is impossible for me to agree with him. He first 



* In certain Acari I have convinced* myself that the nuclei of the blas- 

 toderm result from the division of the germinal vesicle ; but I reserve these 

 observations for future publication. 



