PEMPHIGUS BURSAEIUS. 121 



Koch's* figures of P. bursarius are not happy. 

 Tlieir wing-veining is inexact and defective in drawiDg. 



M. DerbeSjt and likewise M. Lichtenstein,! consider 

 that two years are necessary to produce the complete 

 evolution of the elm-feeding PempJiigince. The last 

 author, in conjunction with M. Courchet, has experi- 

 mented with insects confined under glass cylinders 

 containing grasses growing in moist earth. Up to the 

 present time I believe they have failed to prove their 

 descent to the roots and hibernation thereon. No 

 doubt the artificial conditions rendered necessary by 

 the experiment must present difficulties, but neverthe- 

 less more proof is required before this subterranean 

 habit, connected with assimilation of such diverse food, 

 can be accepted as more than an hypothesis. 



It by no means appears that all Pemphigince require 

 two years for their complete cycle of life. The egg of 

 some species is certainly consigned to the bark of 

 the tree infested, where its vitality has been proved 

 to resist very low temperatures. The warmth of 

 returning spring is only required to bring the young 

 into active life. It is remarkable, however, that the 

 cold of late December will often find the winged 

 females still vigorous, and delivering themselves of the 

 true sexes under the protecting bark. 



This oviposition under the bark has been confirmed 

 by the researches of Messrs. Riley and Monell, who, 

 moreover, think it improbable that any of the species 

 so entirely change their habit as suddenly to feed on 

 such dissimilar food, and to become earth-inhabiters 

 during the winter. § 



In expressing my own hesitation to accept M. Lich- 

 tenstein's hypothesis, I will acknowledge that the com- 

 parative scarcity of species of these Pemphigince in 

 Britain has prevented me from studying them with 



* Koch, ' Du Pflanz. Apbiden.,' p. 293. 

 t Derbes, ' Ann. des Science,' 1. c. 



i Vide Licbteustein, ' Bull. Soc. Ent. de Fr.' (6), iv, 241—24.2. 

 § Riley and Monell, ' Notes on tlie Apliididse of the U. S. of America,' 

 Washington, 1879, 



