70 BRITISH APHIDES. 



In its biology and evolution Phylloxera vastatrix — 

 half aerial and half subterranean, is different from all 

 the other species. According to my views ; the cycle 

 of life is, I believe, as follows. There is but one 

 generation in the year, thus : 



1. The egg, deposited under the bark of the vine in 

 the winter. 



2. The Pseudogyna fundairie, forming galls on the 

 leaves in May and June. 



3. The Pseudogyna migrans, issuing from the galls 

 and descending to the roots. July. 



4. The Pseudogyna gemmans, feeding on the large 

 roots. August. 



5. The Pseudogyna pupifera, feeding on the small 

 roots, where they form tear-shaped swellings. These 

 insects issue from the soil as nymphs, and obtain their 

 wings in September. They fly to the vineyards to 

 deposit their pupae under the leaves, out of which the 

 sexuated forms appear. After union, the female goes 

 under the bark, where she lays her single egg and dies. 

 October. 



But I fancy this simple cycle may be modified in the 

 American insect. It may change under the influence 

 of a climate and food entirely different. Two or three 

 centuries hence may perhaps show the transformation 

 of this species; but even now we witness some altera- 

 tion of habits. In the northern parts of France 

 wherever I have observed the grape- Aphis its evolu- 

 tion is a slow one. It conforms to the above general 

 description with this difference ; that the foundress 

 goes at once to the roots because the leaves of the 

 European vine do not seem adapted to produce galls. 

 Evolution becomes always more rapid as we proceed 

 southwards. Thus, whilst in Germany and Switzer- 

 land the winged form is very rare, and appears in 

 September, I found it at Aix in Savoy in August. At 

 Lyons it appears in July, at Montpellier in June, and 

 Malaga in May. Again, I had roots experimented 

 upon in the hot-houses of the Botanical Gardens of 



