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CONNECTICUT GEOL. AND NAT. HIST. SURVEY. 



[BulL 



center for the most part about the structures indicated in the 

 accompanying diagram (fig. 25). 



For the study of structural characters of value in determining 

 species, reference to the following papers will prove useful (see 

 pages 331-335). Baker (1915), (19171). (1918a); Borner 

 (1908); Cholodkovsky (1915) ; Oestlund (1919a); Patch 

 (1909a); Pergande (1903); Swain (1919a); Tullgren (1909); 

 van der Goot (1915); Vickery (1908); Witlaczil (1882). 



Antennal tubercle 

 Ocular tubercle 

 Thoracic tubercle 



Fig. 25. Diagram of aphid, showing structures used in classification.- 

 Greatly enlarged. Drawing by Dr. Edith M. Patch. 



Key to Genera. 



Fore wings with three oblique veins; the stigmal vein (Rs) want- 

 ing ; M never branched ; cornicles never present ; all generations 



Footnote: The manuscript of this paper was first put into shape for 

 publication in June, 1916. In January, 1920, it was revised. The three 

 years and more during which the paper lay idle have been, systematically 

 speaking, a period of growing pains for the aphids. The species of 

 Phylloxera and Chermes^ after tugging for many years at the apron strings 



