THE CANADIAN ENTOMOLOGIST 371 



such a species as single brooded, while the breeding experiments 

 show conclusively that it is two brooded. The determination is 

 further complicated by the fact that in these species producing 

 summer females, not all the larv?e transform the same season, but, 

 with the exception of a few species, the great majority of the fe- 

 males do not appear u'ntil the following spring. So that the second 

 so-called brood is in reality only a partial brocd; this is a well- 

 established fact in the case of Lygceonematus erichsonii and Pteronns 

 ribesii. In some species there is evidently a partial third brood. 



The pupae of saw-flies do not differ from those of other Hyme- 

 noptera. The antennae, legs and wings are enclosed in separate 

 cases and lie free on the breast of the insect. 



The fact that saw-flies produce only partial second or third 

 broods is also substantiated by the scarcity of adults during July 

 and the following months. This time will vary somewhat, de- 

 pending upon the altitude and latitude of the location. In most 

 regions the adults are found in greatest abundance in May and 

 June. They should be sought on the leaves of plants along the 

 edge of forests, along fences and roadsides, and on the plants of 

 marshy places. 



ADAPTATION IN THE GALL MIDGES. 



BY E. P. FELT, ALBANY, N.Y. 



Adaptation is defined in the Century Dictionary as an "ad- 

 vantageous variation in animals or plants under changed condi- 

 tions." This definition is sufficiently broad to include practically 

 every modification resulting in a variation from what might be 

 construed as the normal for a given family, tribe, genus, or even 

 species. It is well known that every animal is exposed to numerous 

 natural hazards during its life. Existing species must be equal to 

 these perils or become extinct. It is convenient to group the forms 

 of adaptation under three heads. 



L Strength, aggressive and defensive. We can all recall 

 forms which appear well-nigh i'nvincible because of superior physical 

 development — muscular or defensive. The lion and rattlesnake 

 represent two familiar and diverse types belonging in this category. 

 One is remarkable for its superior muscular development and the 

 other possesses a peculiarly efficient m.eans of defense. 



November, 1913 



