VESTIGIAL WINGS AMONG INSECTS. I Si 



longer acted upon by natural selection. This also [is seen in 

 widely separated groups, e.g., Coleoptera (Zoplicrus) and Dip- 

 tera (Ecitomyid), where the wing is simply a slender, hollow bag 

 of very simple structure. 



The fact that in this extremely reduced state they resemble the 

 halteres of Diptera is interesting as affording evidence from 

 another source that the halteres are the vestiges of the second 

 pair of wings which have acquired the new function of equilibra- 

 tion in the Diptera. 



THE CAUSES INDUCING THE ATROPHY OF THE WINGS. 

 Recently Dewitz ('02) has published the results of some ex- 

 periments upon certain wasps (Polistcs], where he succeeded in 

 obtaining artificially, specimens of the Polistcs with abortive 

 wings. These were obtained by subjecting the young larvae to 

 a low temperature for a considerable period, by laying the nest 

 upon a cake of ice. After undergoing this treatment while still 

 young the insects developed only the stumps of wings on attain- 

 ing the adult state. Whether the low temperature in this case 

 acts in a way especially to retard the development of the wings 

 other than by causing a general weakness of the body seems to 

 me very doubtful. The anlagen of the wings are present in the 

 pupa and the last and supreme act of an insect on casting off its 

 pupal skin is properly to expand its wings. If its store of energy 

 has been depleted by untoward conditions during its larval life 

 they are the parts which become abnormal. Thus expansion 

 may take place only imperfectly or not at all if the organism has 

 not vigor enough to expand them. I have known artificial con- 

 ditions of various sorts such as extreme dryness and hot, damp air 

 in closed jars to cause specimens with deformed wings. Under 

 natural conditions such freaks also occur, although much more 

 rarely. During the past summer I have collected a specimen of 

 Ammophila nrnaria and also one of Spkex pennsylvanica, in which 

 the wings were very small and much deformed. Such abnormal- 

 ities are, however, fundamentally different from normally reduced 

 wings and their structure is not constant. Moreover, such 

 sudden variations without corresponding changes in habits can 

 never be preserved by natural selection. 



