60 University of California PuUications. [Entomology 



GENESIS OF VENATION. 



There are two chief groups into which the problems of the 

 origin of venation may be assembled. The first includes the 

 general questions of the formation of venation of the primitive 

 wing and the means and methods for the correlation, modifi- 

 cation, and adaptation of the veins that are the units compos- 

 ing it. The second group comprises the data bearing upon the 

 formation of the special types of venation found in the different 

 orders and families of insects. 



As belonging to the category of general questions, we shall 

 first discuss the theories and conceptions upon which have 

 rested the schemes of venation that have been current. All 

 the earliest systems were based upon the very evident, indeed 

 unmistakable, homologies existing in closely allied forms. 

 Names were given to the veins according to the needs in 

 each particular group, in some cases without regard to the 

 nomenclature employed in other insects. The belief was quite 

 general that there was an essential unit}^ in the venation of 

 all insects, and numerous attempts have been made to apply 

 the terms used in one group to the veins in other groups. The 

 great difficulty of tracing homologies in insects only distantly 

 related accounts for the tangle that has resulted. What these 

 early systems were, we shall not attempt to discuss until we 

 come to consider the modifications in the separate groups. For 

 the present purpose it will be sufficient to say that none of them 

 represents any particular theor}?^ further than the names 

 employed suggest, and that they were simply systems of nomen- 

 clature made for the sole purpose of rendering the wing char- 

 acters available for classification. 



After the general acceptance of the doctrine of evolution, and 

 especially after the promulgation of the theory of (legenbaur 

 as to the origin of the wing, the venation came to be generally 

 regarded as depending for its chief features upon the structure 

 of the organ from which the wing was supposed to have been 

 derived; the conception being, as has already been explained, 

 that the veins are produced around trachea?, and that these, 

 and therefore the veins, simply reproduce the tracheal arrange- 

 ment inherited from the organ that was the precursor of the 

 wing. 



If this view is correct, the surest and best means of study- 



