ANNALS 



OF 



The Entomological Society of America 



Volume XIII JUNE, 1920 Number 2 



Symposium on "The Life Cycle in Insects."^ 



1. APTERYGOTA. 



J. W. FOLSOM. 



University of Illinois. 



In a discussion of the life cycles of insects it is logical to 

 begin with Apterygota because their type of life cycle is the 

 simplest, as it involves no metamorphosis. 



Though Thysanura and Collembola undergo no changes 

 that are sufficiently striking to constitute a metamorphosis, 

 they nevertheless exhibit in their postembryonic development 

 various minor changes of structure and coloration. 



For example, Lepisma saccharina at hatching is whitish; 

 is a slender creature, on account of its narrow thoracic segments; 

 and does not have as yet the characteristic styli of the eighth 

 and ninth abdominal segments. The antennae have only 22 

 segments, though they later develop some 60 or 70 subsegments; 

 and the lateral cerci have at first only 10 segments. Lepisma, 

 as it emerges from the egg, has no scales. Even the first molt, 

 which occurs seven days from the time of hatching, brings no 

 change in these respects. (Heymons.) 



In Collembola, at hatching, the head is large in proportion 

 to the body — much as in a grasshopper. As the individual 

 grows there are changes in the relative lengths of the segments 

 of the body and of those of the appendages. Thus, in Tomocerus 

 vulgaris, comparing small and large individuals: 



*Presented at the St. Louis meeting, December, 1919. 



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