136 Annals Entomological Society of America [Vol. XIII, 



by keeping the insect in darkness, as in the case of Anurida. 

 On the other hand, the embryo Anurida develops pigment 

 prematurely if the egg is exposed to sunlight. 



The colors and color patterns of Collembola are not known 

 to have any adaptive significance. Many Collembola resemble 

 their environment in color, to be sure, but there is no evidence 

 that this resemblance is of any advantage to the organism. 



The most conspicuous fact in regard to the seasonal history 

 of Collembola is their tolerance of low temperatures. Many 

 species are active in winter when most other insects are not. 

 Some species grow and molt during winter, and lay eggs at low 

 temperatures. Thus one species was seen to lay eggs at 0° C. 

 The temperature-range of activity is lower than that of other 

 insects. Thysanura, on the contrary, are far less tolerant of 

 cold. Some of them hibernate but do not grow, molt, or lay 

 eggs in winter. Thysanura are not known in the Arctic region; 

 though the arctic and subarctic Collembola number some 

 seventy species. 



Apterygota molt at frequent intervals throughout life; are 

 long-lived and have therefore many molts; the number being 

 indefinite. 



In Collembola, ecdysis is something more than a provision 

 for growth; occurring as it does after growth has ceased; and 

 being, in part at least, an excretory process. With each molt 

 the inner half of the epithelium of the mid-intestine is cast off 

 and discharged from the food canal, and with it are expelled 

 pseudocrystals of sodium urate, which have previously accu- 

 mulated in the epithelial cells. This process is correlated with 

 the absence of Malpighian tubes in Collembola. 



Apterygota best illustrate simplicity of the life cycle. They 

 are relatively simple in structure, development and habits, in 

 correlation with their environment, which is relatively simple 

 and remains constant. The functions of growth and repro- 

 duction are not sharply separated as they are in Pterygota. 

 Apterygota, being primitively wingless insects, show none of 

 the specializations associated with the presence of wings; such 

 as a firm integument, differentiation and consolidation of the 

 thoracic segments, and the development of various thoracic 

 sclerites in relation to muscles of locomotion. Neither are there 

 found such extensive modifications of the abdomen in relation 

 to reproduction, as occur in pterygote insects. 



