16 SOME ASPECTS OF MORPHOLOGY 



The morphology of the neck region and the cervical sclerites is 

 extremely difficult to interpret, and many speculative views have 

 been advanced to explain it. It is obvious that if the post- 

 occipital suture marks the division between the maxillary and 

 labial segments, the tergal region of the latter segment is repre- 

 sented by the narrow band-like area behind this suture, and 

 forms the greater part of the boundary of the occipital foramen. 

 The fact that the dorsal muscles of the prothorax pass through 

 the neck and are attached anteriorly — not to the posterior 

 margin of the labial segment, but to the post-occipital ridge 

 beyond — appears to be a morphological fact of importance. 

 This relationship has led some morphologists to conclude that an 

 intersegmental region has become deleted somewhere in the 

 neck. The cervical sclerites are consequently regarded as dis- 

 membered portions either of the labial segment or of the prothorax. 

 Other morphologists maintain that the neck itself is the greatly 

 enlarged intersegmental region, and that the cervical sclerites 

 are sclerotised areas which have developed in the membrane of 

 that region. 



A. 



2. Wing Venation 



The determination of the origin and homologies of the wing 

 veins has, in the past, been embarrassed by the various systems 

 of nomenclature employed by different workers. As a rule, the 

 terminology of an author was only applicable within the limits of 

 the particular group or order of insects which he studied. The 

 establishment of these different systems has been the inevitable 

 outcome of specialised studies, uninfluenced by modern conceptions 

 of evolution. These defects could scarcely be remedied at the 

 time because no criterion had yet been explored upon which 

 homologies might have been based. Such deficiencies have been 

 realised for more than forty years, and it was in 1886 that 

 Redtenbacher published an important and well-illustrated 

 memoir in which he proposed a uniform system of venational 

 nomenclature ; he named the veins costa, subcosta, radius, 

 media, cubital and anal respectively. Redtenbacher, furthermore, 

 reaffirmed the importance of the fact that the main veins primi- 



