380 THE CANADIAN ENTOMOLOGIST 



very distinct (fig. 31). They are more prominent upon forms 

 taken in the summer than in the spring forms. 



Genus Pterocomma. 

 All the species of this genus show the same character of these 

 .organs. There is a large group of very small pores close to the 

 base of the femur. Popnlifolice Fitch (fig. 33) and smithies Mon. 

 (fig. 34) show very compact groups. Salicis L. (fig. 35) shows 

 numerous pores upon the trochanter and a group of nine or ten 

 near the base of the fore wing (fig. 36). Bicolor Oest., (fig. 37) 

 has a similar group upon the femur. 



Genus Trichosiphum. 



One species of this group has been examined and it possesses 

 one large pore near the base of the femur (fig. 46). 



Genus Aphis. 



There is considerable variation met with in this genus. Most 

 species have two or three of these organs at the base of the femur. 

 A. coreopsidis Thos. (fig. 21) has a group of four or five at the 

 base of the femur. A. gossypii Glover (fig. 32) is quite s'milar 

 as is also A. viburnicola Gill (fig. 45). A. madiradicis Forbes 

 shows a group near the base of the fore wing (fig. 22) and a group 

 of four or five at the base of the femur. A. middletoni Thos., 

 shows a group near the base of the fore wing (fig. 24), and about 

 five near the base of the femur (fig. 25). It will be remembered 

 that these last two species are subterranean. A. maidis Fitch, 

 shows one of the deepest pores seen on any species (fig. 26). This 

 huge pore is, however, not present on every specimen. The same 

 thing is sometimes met with in species of Lachnus. 



Genus Myzus. 



Myzus cerasi Fab. shows one or two pores at the base of the 

 femur, and M. plantaginis Fab., has a group of about four near the 

 base of the hind wing (fig. 28). 



Genus Marrosiphum. 

 M. circiimflexum Buckton, possesses a scattered group of 

 about six small pores on the femur (fig. 27). Noneiis^found upon 

 the wings, or if so a few small ones along the subcosta. M. am- 

 hrosicE Thos., has one pore at the base of femur and a few minute 

 ones along the subcosta of the wing. 



