I 82 CHARLES T. BRUES. 



Dewitz l associates a diminution of the oxidation processes in 

 the body with the wingless condition, which is borne out by the 

 comparative anatomy of the tracheal system, but as to which is 

 cause and which effect it is not so easy to decide. As actively 

 flying insects require more air to aerate their blood, they natur- 

 ally have more extensive tracheae and respiratory sacs to supply 

 it, so that it seems only proper to consider that in isolated genera 

 or species among a winged group of insects it is the wings and 

 not the tracheae hidden inside the body which have first been 

 influenced by external conditions and caused to change their form. 



In the case of males of certain species which are winged 

 while the females are wingless the short life of the male and the 

 necessity of his seeking the female are sufficient to account for 

 the female being the sex to lose the wings first in becoming 

 adapted to the environment. 2 



It has long been recognized that insects inhabiting certain 

 regions are more apt to be wingless or subapterous than their 

 relatives living under other surroundings ; notably the forms 

 inhabiting oceanic islands, mountain tops and of deserts or arid 

 regions tend to have the wings short or wanting. These seem 

 to be the only anomalous cases, for all others can be traced to 

 parasitism or secluded environment. The well-known explanation 

 of Wallace that the great numbers of insects blown out to sea 

 and thus destroyed has caused forms that do not fly or are 

 wingless to be saved at the expense of the more active forms, is 

 regarded by Dewitz ('02) as having little weight. It is true that 

 actual observations upon this point are not numerous, but the 

 immense numbers of dead insects that are often cast up on 

 beaches after a severe storm show that this must be a very 

 important factor. Needham ('oo) has given interesting data 

 upon this subject in a recent paper on the insect drift of Lake 

 Michigan in which he describes the enormous numbers of insects 



O 



cast up on certain portions of the beach of Lake Michigan. 3 



Isolated mountain peaks present similar conditions, although 

 here the mortality can not be so great. A windstorm in such 



1 Loc. at. 



*See also note under Diuelus, page 187. 



3 Leconte has described similar phenomena on Lake Superior beaches. 



