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



locular egg-tubes are Aphis Quercus and A, platandides^, the 

 wingless females of which exhibit three (and A. platano'ides even 

 four) deposits, representing eggs, in the individual egg-tubes. 

 (Dr. Claus of Marburg has also met with wingless females with 

 plurilocular egg-tubes, in two apparently unnamed species of 

 Aphis from Betula alba.) 



If this latter observation were not sufficient of itself to efface 

 the distinction which apparently prevails, with regard to the 

 formation of the egg-tubes, between our Bark-lice and the other 

 true Aphides, I must further indicate that the second, superior 

 germ in Chermes (especially in Chermes Laricis, fig. 1) is not 

 unfrequently formed only at a later time, or not until the pre- 

 ceding egg approaches its perfect maturity; that therefore, 

 under such circumstances, the same egg-tube may consist some- 

 times of one and sometimes of more chambers, according to the 

 age and state of development of its contents f. Moreover the 

 eggs in the different tubes arrive at maturity at different times, 

 so that tubes of one and two chambers may not unfrequently be 

 met with together in the same ovary. In the same way, at cer- 

 tain times, the tubes of Phylloxera consist only of two chambers J, 

 those of Aphis platano'ides of three, &c. 



Although, therefore, the distinction between the unilocular 

 and plurilocular egg-tubes does not appear to be very great, 

 still, on the other hand, it is not to be altogether disregarded. 

 This is most distinctly evidenced in the different destiny of the 

 superior clavately-inHated extremity of the egg-tube, which, with 

 its peculiar cellular corpuscles, has sometimes been regarded as 

 a proper superior chamber. In the Plant-lice with unilocular 

 egg-tubes this terminal piece, with its contents, is gradually lost 

 during the evolution of the egg-germs; in the species with 

 plurilocular egg-tubes it remains unchanged, just as it was with 

 the first egg-germ, without ever diminishing perceptibly in size 

 or becoming aborted. 



* Dr. Claus called my attention to the fact that the nurses of this spe- 

 cies are not unfrequently attached after death to the surface of the leaves 

 inhabited by them, by means of a rather large convex disc. On closer 

 examination I recognized in this disc the cocoon of a larva which, from 

 its appearance, would probably be that of an Ichneumonidous insect. This 

 larva lives, up to the time of its change to the pu})a state (and indeed 

 always singly), as a parasite in the Aphides, but afterwards breaks through 

 at the ventral surface, and then spins its cocoon between its previous host 

 and the surface of the leaf. 



f This is also in accordance with the fact that the egg-tubes of our spe- 

 cies of Chermes (C Abietis) are at first developed as simple tubes, exactly 

 in the same way that I have described for the egg-tubes of Aphis and 

 Coccus. 



X Individual egg-tubes of C. Abietis also now and then exhibit a third 

 egg-rudiment. 



