222 Maine Agricultural Experiment Station. 1920. 



The overwintering egg is thus true to the traditions of the 

 Hexapods, but with it ends all conventional observances, for 

 between one such egg and the next in sequence there are crowded 

 such phenomena as a succession of parthenogenetic viviparous 

 generations ; extreme examples of polymorphism ; alternation 

 of generations in a series where a duplication may not occur for 

 seven or more generations ; parallel series in which certain 

 females give birth to true sexes without beaks while others of 

 the same generation give rise to normal young which hibernate 

 in the first instar without feeding; and a system of seasonal mi- 

 gration which is not surpassed by any other in the animal king- 

 dom. That all these divergences from the ordinary life cycle 

 for insects take place within the limits of the family Aphididae 

 would seem remarkable indeed ; but it is no less than appalling 

 to realize that the total range of phenomena just indicated may 

 be exhibited by a single species. 



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, antennae and legs, exhibiting in this atrophy 

 of those organs of orientation and locomotion, a transformation 

 which has to do with the loss of such organs as characterized 

 them as insects in the first instar, rather than in the acquisition 

 and development of the structures of an adult hexapod. This 

 metamorphosis by reduction, associated with the complete ab- 

 sence of wing development in the female is correlated with the 

 sedentary habit of this family and is in line with the atrophy of 

 class structures in parasitic animals. But the suppression of 

 generalized characters does not inhibit the appearance of special 

 structures of a high degree of development, as is beautifully 

 illustrated by the wax glands, marvelous in form and variety, 

 to be found in the coccids ; a concentration of structural effort 

 directed toward the secretion of a waxy protection for these 

 sedentary creatures and their eggs. 



