518 W. L, TOWER, 



SwAMMERDAM (1732—1738), REAUMUR (1734), Lyonet (1760) and 

 others all found the partly developed imaginai organs present in the 

 late larval stages of various insects. As a result of these discoveries, 

 the fantastic theories, which had been held by the earlier authors 

 concerning the relation of larva, pupa and imago in insect meta- 

 morphosis, were replaced by a more rational account of the post- 

 embryonic development of insects. 



Although, in this period, the advance made in knowledge con- 

 cerning insect metamorphosis was great, the new explanation was still 

 but a rough approximation of the truth, and it was clothed in a 

 theoretic garb quite as fantastic as that of the earlier authors. Only 

 the late stages in the development of the imaginai organs were seen; 

 and, in ignorance of their origin and early development, it is not to 

 be wondered at that the observations made were regarded as strong 

 positive evidence for the truth of the "encasement theory". 



Through the latter half of the eighteenth century and the first 

 half of the nineteenth no further advance was made towards an ex- 

 planation of the origin and development of the imaginai organs of 

 insects. Each observer repeated the work of his predecessors, and 

 no one succeeded in discovering the younger stages. 



The publication of Weismann's papers (1864—1866) upon the 

 post-embryonic development of Musca and the enunciation of the 

 theory of metamorphosis by "imaginai discs" and the "histolysis" of 

 larval tissue, form a starting point from which is to be dated a con- 

 siderable body of observations upon the many phenomena concerned 

 in insect metamorphosis. Of the adult insect structures whose develop- 

 ment has been traced in the last forty years few have received 

 more investigation than the wings. The evident importance of these 

 organs to insects, and the taxonomic value assigned to them have 

 made them the objects of much research and controversy. However, 

 the major part of these studies have been made upon Lepidoptera, 

 and thus, while the origin and development of wing in the higher, 

 specialized forms is fairly well known the lower and more generalized 

 orders have not been studied, and Rehberg's (1886) paper still re- 

 mains the only considerable attempt to trace the early development 

 of the wings in any heterometabolic insect, and this paper is wholly 

 inconclusive. 



The following paper contains the results of a research made to 

 determine the origin and development of the wings of Coleoptera. 

 This research was begun in the Zoological Laboratory of the Museum 



