40 



HALF HOUES WITH IXSECTS. 



[Packard. 



they belong, such as the mealy bug of our hot-houses or 

 Cochineal insect of tropical countries and the Aleurodes, in 

 which the sexual differences are less marked, and then com- 

 . paring them with the aphides on 



the one hand, and on the other 

 the Ps3"lla, a member of another 

 family closely allied, we are en- 

 abled to see that the changes 

 >:^ ,»c<^^p^j^^^^^^-^^^^ , inform have been undoubtedly 



induced by differences in habits, 

 the kind of surface to which the 

 scales are attached, the species 



-, i_(^ of tree to which they belong, as 



well as to the different degree 

 of mobility of the female ; for the 

 more she is fixed and immov- 

 able, the more active and lively 

 is the male, just as in St3dops 

 Femaiestyiops ^^ b ec-p ar asi te , the female 



(Fig. 30) is remarkably different from the agile, volant male 



(Fig. 31). We may see in the aphis, where the two sexes 



are alike, that in their ^^^ 3^^ 



coui'tships the male 



finds its active partner 



in the ordinary move- \1^&^ 



ments of life, while 



since the female scale V -— --^^^^"■'■'/"'^|u|l 



insect is immovable, \ x/l' Eirfi 



its winged partner 



needs to be far more 



restless and swift in 



its movements than 



., 1 1 . Male Stylops. 



the male aphis ; so 



that its chances of encountering its mate in the course of 



its travels, and thus providing for the continuance of the 



