36 



to dogwood and back less clearly defined, but such a dimorphism, if we 

 may call it so, is not without parallel, and does not seem unreasonable. 

 There seems reason to believe that while a large proportion of the 

 pseudogynes acquire wings of perfect development, and migrate to dog- 

 wood, that there is also another portion in which the wings for some rea- 

 son fail to develop, and these from necessity remain on the roots or at 

 best remain near the surface of the ground, and the sexual generation 

 produced by them at the same time as from the winged ones, or perhaps 

 a little later develop by feeding upon grass roots, and deposit their eggs 

 where they have themselves developed. As to whether these eggs are 

 as successful in their further development as the ones deposited on 

 Cornus remains for further observations to determine. Possibly in cer- 

 tain seasons they may survive better, and thus provide a double means 

 for the preservation of the species. As to the conditions which might 

 affect the acquisition of wings we can do little more than speculate, but 

 it seems proper to call attention to the possible elements that may fur- 

 nish a solution. 



The day before the first swarming of Schizoneura (1.4th) had been 

 very warm in the middle of the day, with a heavy shower in the latter 

 part of the afternoon, followed by a steady rain in the fore part of the 

 night, and this by a sharp fall in temperature, so that the morning of 

 the 15th was clear and cold (possibly a slight frost). The day remained 

 cold, but was bright and sunny, and the swarming observed occurred in 

 the latter part of the afternoon. Some other aphids were observed on 

 the wing, but very few as compared with the swarms of corni. 8. corni 

 was seen in the air on subsequent days, but comparatively scarce till, 

 again two weeks later (29th), after a very similar condition of weather 

 (warm, with rain, followed by cold), when another swarming occurred. 

 In ow, it may be that those individuals, which are at a certain stage when 

 such conditions occur, are enabled to acquire wings while those less fully 

 developed remain without the full expansion of these appendages. 



In comparing the two forms infesting grass roots and dogwood, re- 

 spectively, I have studied great numbers of wingless individuals, 

 winged forms and apterous males and females, and have come to the 

 conclusion that they must all belong to the same species. It will, how- 

 ever, be in place, I think, to place in position for comparison the differ- 

 ent descriptions which have been given of the species to show that, 

 notwithstanding the terms used by different authors, and their wide 

 separation in time and place, there is no real discrepancy in them. The 

 original description by Fabricius is very short and general, and is as 

 follows (Ent. Syst., IV, p. 214, No. 19) : 



Corni. A. Corni sanguineae. 



Habitat in Corni sanguiueai foliis. 



Corpus nigrum abdounne basi et subtus virescente. Pedes nigri. Anus absque stylo 

 et corniculis. 



Juniores pallidi macula magna, dorsali, nigra. 



