1920] Fracker: Lepidoptera 167 



The sedentary habits of the female scales leave the natural 

 dispersal of these insects to the first instar larvae so that, except 

 for accidental carriers, the spread is characterized by its 

 thoroughness rather than by its breadth. 



The most congenial conditions for the coccids are found in 

 warm climates, and there are comparatively but few species 

 whose life cycles are attuned to regions having severe winters. 



5. THE LIFE CYCLE OF THE LEPIDOPTERA. 



S. B. Fracker, 

 Madison, Wis. 



Coming, at the point in this program between discussions of 

 heterometabolous and holometabolous developrqent, it seems 

 necessary for us to diverge a few moments from the subject as 

 printed, to consider the biological significance of complete 

 metamorphosis. 



The structural basis for the distinction between these two 

 types of development has been repeatedly described. Studies 

 histological, morphological, and physiological, have been made 

 on the ontogeny of the different parts of the insect body, in 

 ametabola, heterometabola, and holometabola. Uniformity 

 has been discovered in wing development, cell structure, and 

 body sclerites within each of these groups until we may say 

 that the basis for the three great subclasses of insects rests on a 

 solid foundation in morphology. 



The biological significance of these groups, on the other 

 hand, has usually been overlooked. The environmental prob- 

 lems which evolution is called upon to solve, if we may be per- 

 mitted to express the situation in this way, become immensely 

 complicated as the number of different forms taken on by a 

 single individual increases. 



Speaking biologically then, insects without metamorphosis 

 exist in, and are thus adapted to, a single environment, both 

 the form and the surroundings remaining the same throughout 

 the Hfe of the individual. With the arrival of wings, an increase 

 in the number of activities causes an enlargement of horizon 

 and introduces some degree of variety in the character of the 



