University of California Publications. [Entomology 



PART L— WINGS. 



ORIGIN OF WINGS. 



The wings in insects that have simple metamorphosis very 

 evidently arise as outgrowths of the body wall of the thorax, 

 as has been well understood by all entomologists, and described 

 by even the oldest writers. Their development in the higher 

 orders, however, is much more obscure, though the presence of 

 the wing rudiments beneath the skin of the larvae in the 

 higher insects has been known since the days of Swammerdam 

 (1737-38). The earlier authors quite naturally considered 

 these latter to be entirely different in structure and origin from 

 the wingpads of the lower insects. Weismann ('66) was the 

 first to discover the connection between these internal wing 

 rudiments and the hypodermis of the body wall, but even he 

 believed this to be true only in certain insects (Nematocera). 

 Later, Kiinckel d'Herculais ('75) showed that, in the groups 

 supposed by Weismann not to have the fundaments of the wings 

 connected with tlie hypodermis, there was, nevertheless, evi- 

 dence of such an origin. All subsequent authors who have 

 investigated the subject, with the exception of Landois ('74), 

 Ganin ('76), and Graber ('89), have accepted the idea of the 

 hypodermal origin; as no one of these three were able to dis- 

 cover any other source, all the positive evidence is to the effect 

 that the wings in all the groups, those with complex metamor- 

 phosis as well as the others, arise as a modification of the cells 

 of the hypodermis of the thorax. 



From this ontogenetic fact the conclusion can be drawn with 

 much confidence that, in the primitive insects also, the wings 

 arise as outgrowths of previously undifferentiated portions of 

 the hypodermis of the thoracic segments. To some extent, 

 especially in the lower insects, as will be shown hereafter, the 

 ontogeny does not exhibit a direct development toward the 

 imaginal wing. There is a great deal of evidence, as will also 

 be shown below, to the effect that the wing in its first develop- 

 ment followed likewise an indirect course; that is, in passing 

 from the first differentiation of the skin structure to that found 

 in a perfected wing, the cells assumed functions and developed 



