M. Leuckart on the Reproduction of Bark-lice. 413 



In the small treatise on Parthenogenesis already repeatedly 

 cited, I have referred to this superior portion of the unilocular 

 egg-tubes in the Aphides as the " vitelligene ;" and indeed its 

 resemblance to the vitelligenes of the plurilocular egg-tubes 

 described by Stein is unmistakeable. Supposing this interpre- 

 tation to be correct, all analogy would lead us to expect that a 

 vitelligene of this nature would be repeated between each two 

 egg-germs in the plurilocular egg-tubes of our plant-lice. But 

 this is not the case. The Aphides with plurilocular egg-tubes 

 also possess only a single vitelligene, and this only at the upper 

 end of the egg-tubes (fig. 1). 



This circumstance must render it doubtful, notwithstanding 

 any similarity, whether it be correct to regard the terminal piece 

 in question as a " vitelligene.'^ We might now suppose, with 

 apparently greater justice than previously, that the structure in 

 question is a so-called germigene, and regard the individual 

 cellular corpuscles in its interior as egg-germs ; and this per- 

 haps might be done the more readily, as the compartment in 

 question resembles, in the formation and appearance of its con- 

 tents, the terminal piece of the so-called germ-stock in the vivi- 

 parous Aphides, the individual cellular corpuscles of which, 

 according to Leydig, become converted directly into the future 

 germs. In this way, therefore, we may establish an analogy 

 between the genitalia of the viviparous and oviparous Aphides, 

 which may also perhaps, in another respect, serve as a guide for 

 the comprehension of the entire mutual relation of these two 

 forms of individuals. 



I admit that I do not regard this question as yet ripe for 

 decision. It is certain that, from our present observations, the 

 consideration of this terminal piece as a germigene is somewhat 

 seductive ; but the aspect and nature of the cellular corpuscles 

 in its interior are different from those ordinarily met with else- 

 where in the germigenes of insects ; and, moreover, I have never 

 yet succeeded (nor, indeed, with the viviparous Aphides) in con- 

 vincing myself by direct observation of the conversion of these 

 cells into egg-germs. On the contrary, we may detect certain 

 differences in size, behaviour towards reagents, &c., between the 

 germinal vesicles of the youngest ova and the nuclei of these 

 cellular corpuscles (which, nevertheless, must be identical if the 

 latter are to be regarded as egg-germs), such as are scarcely in 

 favour of any such assumption. Thus, for example, in Lecanium 

 Hesperidum I found the germinal vesicles of the youngest ova 

 0*02 millim, in diameter, whilst the nuclei of the cellular cor- 

 puscles in the terminal compartment measured 0*037 millim. 

 In Coccus Hesperidum the germinal vesicle, at a still earlier grade 

 of development, was 0*009 millim., also smaller than the nuclei. 



