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



which measured 0*013 millim. The same thing applies to the 

 Aphides. To this we must add the fate of these cellular cor- 

 puscles in the unilocular egg-tubes of the Aphides and Coccina, 

 which is also scarcely in favour of the opinion that they are 

 converted into egg-germs, although indeed cases of abortive 

 egg-germs are not very rare. 



On the other hand, the interpretation of the compartment in 

 question as a " vitelligene " appears by no means to be contra- 

 dicted by its simplicity in the plurilocular egg-tubes of our 

 Aphides. We certainly must not assume, as Stein does, that in 

 the case in question the granular yelk is exclusively furnished by 

 the cells of the vitelligene. This one-sided interpretation may 

 probably find but few supporters at the present day. I think 

 we have arrived pretty generally at the opinion that, besides 

 the cellular corpuscles of the vitelligene, the ordinary epithelial 

 cells of the egg-tubes also take part in the deposition of the yelk. 

 This part is indeed probably only a subordinate one ; but in our 

 Aphides it may suffice for the completion of the maturity of the 

 egg, the rather as the contact with the terminal compartment is 

 not interrupted until a somewhat late period — indeed not until 

 the yelk has already grown to a very considerable mass. 



With regard to the histological structure of the egg-tubes, 

 there is nothing particular to mention, unless it be the circum- 

 stance that our Bark-lice closely resemble the other Aphides in 

 the great number of the cellular corpuscles occurring in the 

 terminal compartment. Between these and the structureless 

 proper membrane we not unfrequently see a delicate epithelial 

 layer, which, however, also occurs in the same place in the allied 

 animals, and does not appear to be by any means deficient even 

 in the viviparous Aphides. The process of egg-formation is ex- 

 actly the same as described by me in Aphis and Coccus. Even 

 the short and solid peduncles adhering to the inferior pole of 

 the egg-shells in Chermes constitute no characteristic distinction 

 of our animals, since I have found the same structure on the 

 eggs of Aphis Quercus and A. platano'ides*. 



With regard to the number of egg-tubes in the ovaries of 

 our Bark-lice, we find very considerable discrepancies, not only 

 in different species, but also in the different winged and wing- 

 less individuals of the same species. In the latter respect it 

 prevails as a law — if we may judge from C. Abietis and C. Laricis 

 — that the winged individuals, as they are on the whole of a more 

 slender structure, also possess a smaller number of egg-tubesf. 



* It may be mentioned here, in passing, that the small winged males of 

 A. platano'ides possess three perfectly separated, pyriform testicular tubes 

 on each side. 



f This also appears to apply to the winged and wingless viviparous 



