XXV 



and has been thought to be viviparous, is only a larval form, and like all 

 larvae it produces without any fecundation (as it is sexless) the subsequent 

 form. 



" While, however, a larva is general!}' monothalamous, and gives birth 

 only to another larva, pupa, or winged form, the aphid ian larval form is 

 polythalamous and produces many germs. 



" On the other hand, aphidian females are also very often (in Phylloxera, 

 Tetraneura, Vaccuna, Sonizoneura, Pemphigus) monothalamous, that is to 

 say they lay only a single egg, while all insects wliich have only one larva 

 produce a large number of eggs. 



" It is perhaps not easy to imagine a larval form more perfect in its 

 organization than the adult female form, yet this is the case. We know 

 already many genera [Lampijris, Driliis, Psyche), where the female looks 

 quite like a larva, while in aphidians we get a larva more perfect in 

 appearance than the imago, as it has wings and rostrum, which are often 

 absent in the perfect female. But there is always this difference — the larva 

 has no accompanying male form and produces no eggs, but only buds or 

 gemmations. The egg is fecundated only by external influence, the bud 

 or gemmation develops without any external aid. The gemmation can 

 assume the most variable forms of maggot, nymph, &c., the egg keeps 

 always the known ovoid form more or less spherical ; the gemmation can 

 even assume the form of an egg, and actually does so in some few aphidians 

 (I know of no other instances except in Phylloxera), but the faculty of 

 developing^ without any fecundation, and being the produce of a larval form 

 without any corresponding male, indicates the true nature of that pseud- 

 ovum. The biological cycle of the aphidians consists of the usual four 

 stages of life, viz. first and second larvae, nymph, and imago, but each of 

 these stages is subdivided into four moults, and terminates by a form 

 capable of gemmation, and having the appearance of a female imago. 

 I would suggest for them the name of Pseudogyne. These Pseudogynes 

 appear generally apterous in the first and third stages, and winged in the 

 second and fourth. In this last stage they furnish the sexual forms, and 

 their gemmations are true pupse, from which male and female forms shortly 

 issue to copulate, and after fecundation the female lays its simple egg, and 

 the cycle begins again. 



«' I shall have the honour to forward shortly to the Society the complete 

 relation of the history of Phylloxera [Peritytnbia) vastatrix, wherein the 

 present ideas are more fully developed ; but I thought that it would perhaps 

 interest my colleagues to have this preliminary communication of the results 

 of my breedings. 



" The last discovery I have made is that of the sexual forms of Pemphigus 

 spirotheccE. I obtained the winged pupiferous Pseudogyne from its galls in 

 December, and it deposited its pupte in a glaso tube on the 19th of that 



