M. Leuckart on the Reproduction of Bark-lice. 325 



takes place in both generations by a parthenogenetic process, by the 

 spontaneous development of the eggs. 



Although I have examined fully two hundred of our animals, 

 I have never met with a male among them. All the individuals, 

 wingless and winged, large and small, were females, and, indeed, 

 virgin females. This was the case not only with animals taken 

 before oviposition, but also with those engaged in depositing 

 their eggs, and even with those whose eggs already presented 

 distinct traces of the commencement of evolution, or even con- 

 tained developed embryos. More than once I isolated the eggs 

 of such virgin animals, and afterwards saw them hatch. 



After such observations, there can be no doubt that the Fir- 

 lice generally propagate without males. But whether males are 

 entirely wanting, or whether they merely make their appearance 

 from time to time, under certain favourable circumstances, and 

 then fecundate the females, I must leave undecided; yet it 

 almost appears to me as if certain anatomical conditions, to which 

 I shall have to refer hereafter, rendered the first supposition to 

 a certain extent credible. 



It is, however, not only the common Fir-louse (0. Abietis) 

 that behaves in this manner. Towards the end of April I several 

 times observed on the young shoots of the Fir a wingless Louse 

 (C. Picece, Eatzeb. ?), which presented an extraordinary resem- 

 blance to the individuals of the first generation of C. Abietis, but 

 was distinguished therefrom partly by its darker, almost black 

 colour, and partly by its far smaller size. I can state nothing 

 with regard to the mode of life of this species : I afterwards 

 sought in vain upon the infected trees for galls, and must leave 

 it undecided whether our animal, like C. Abietis, subsequently 

 produces a second winged generation; this, however, is very 

 probable. But I am certain that all the individuals examined, 

 amongst which were several with eggs already deposited although 

 not numerous, proved to be unfecundated females, exactly as in 

 the corresponding state of C. Abietis. 



I can assert the same thing of the nearly allied Phylloxera 

 coccinea, Von Heyden, of which I met with numerous wingless 

 females, at the commencement of July, on the lower surface of 

 oak-leaves, with eggs deposited in rings. In this case, also, the 

 older eggs (about 30-40 in number) contained an embryo al- 

 ready far advanced in development, although no trace of semen 

 was to be detected in the mothers. Previous observers have 

 overlooked the existence of this first generation of wingless 

 females : they speak of winged animals which made their ap- 

 pearance in August and September, and fastened their eggs to 

 the oak-leaves exactly in the same way as the wingless females. 

 Unfortunately, I have not succeeded in finding these winged 



