162 Annals Entomological Society of America [Vol. XIII, 



tide over the period of famine; and in the North some non- 

 migrating species produce the sexes in August, July or even 

 June on exhausted vegetation. 



The parthenogenetic type of reproduction, correlated, as it 

 were, with the abbreviated time required for the development 

 of the individual, makes possible the enormous increase of the 

 aphid colony and at the same time minimizes the numerical 

 importance of the gamogenetic egg. We find, then, one of the 

 very striking differences between these and other insects, in 

 the fact that the oviparous female of the aphid never deposits 

 more than a few eggs and in certain tribes one egg only of this 

 character is produced. As if to further emphasize the signifi- 

 cance of parthenogenesis for the aphid, certain species (as 

 Eriosoma lanigera and Prociphilus tessellata) even when dwelling 

 in the North, attempt to provide for a continuation of the 

 apterous, viviparous, parthenogenetic part of their cycle by 

 producing annually nymphs to hibernate about the base of the 

 secondary host at the same time that the migrants are producing 

 the sex forms on the primary host.* 



COCCIDS. 



The eccentricities of the coccids are concerned with the 

 specialization of their structural characters, and the modified 

 metamorphosis of both sexes rather than with any striking range 

 of habit or peculiarity in sequence of generations; since their 

 typical life cycle comprises between one fertilized egg stage and 

 the next but a single generation composed of both sexes. The 

 extreme possibilities of coccid metamorphosis are illustrated 

 by those species in which the females, at their first molt, lose, 

 for good and all, eyes, antennas and legs, exhibiting in this 

 atrophy of those organs of orientation and locomotion, a trans- 



*In the preparation of this paper repeated attempts have been made to broach 

 the aphid cycle in general terms, a process that would force us to build upon a 

 hypothetical type reminiscent of a primitive condition when each generation was 

 -composed of males and females, both alate, and when propagation was solely by 

 means of the gamogenetic egg as is typical for the class Insecta; but not only is 

 such a lost type hypothetical for the aphids, but the processes of divergence have 

 been so marvelously complicated, as concerns structure, habit, and sequence and 

 combination of generations, that the hope of correlating the different groups on 

 any graphic basis has been abandoned; and representative glimpses are all that 

 the accompanying outlines offer. 



Appreciative thanks are due Dr. A. C. Baker, Dr. O. W. Oestlund and Dr. 

 Herbert Osborn for reading the paper critically and for certain suggestions that 

 have been incorporated. 



