NO. 1 087. THIH THORAX OF INSECTS— SyODGRASS. 513 



should be taken as tlie Liniiivus of thoracic nomenclature, and there 

 is not siillicient reason on any ground for applying new terms to 

 the parts he named. 



In the study of the wings the venation nomenclature established 

 1)3' Comstook has been adopted. No attempt has been made to prove 

 or to disprove Comstock's interpretations of the veins in (he main part 

 of the wing. While a study of the basal structure may show definitely 

 that some ]:)articular vein is absent as a distinct trunk at the base, 

 it still remains an open question whether this vein is actually gone 

 or is fused with the one before or behind it. The general venation 

 must furnish the evidence in most such cases. 



II. THE SEGMENTATION OF THE HEAD AND BODY. 



A few decades ago an insect was defined as a creature consisting of 

 a head, a thorax subdivided into three segments, and an abdomen 

 composed of 10 or 11 segments. Such a definition, however, would 

 not satisfy the demands of most ])rescnt-day entomologists, and it is 

 interesting to contemplate the shock some antievolutionary forefather 

 of entomology would receive could he now see in print the statement 

 that an in.sect is composed of 40 segTOents. This said forefather 

 might be in some measure pacified, however, were he to learn that the 

 insects themselves have not been required to keep pace with the ideas 

 of entomologists concerning them. 



1. Segmentation of the Head. 



If the question as to how many embryonic metameres form the head 

 of an insect could be decided by a vote among present and past 

 students of the subject, the six-segment theory would undoubtedly be 

 established. The problem of head segmentation has been attacked 

 from both an anatomical and an embryological standpoint, but, 

 since the embryologists attempt to discover the actual facts of de- 

 velopment, it would seem that deference should be paid to their 

 opinions. Furthermore, the embryologists agree more closely among 

 themselves than do the anatomists. Although the number of head 

 metameres claimed by the former varies from four to seven, this dis- 

 crepancy is not what it appears to be in figures, for the chief point of 

 disagreement is whether the three preoral segments apparent in the 

 embryo are actual metameres or are only secondary divisions. The 

 real question is thus reduced to one between six' and seven segmejits. 



On the other hand, the anatomists describe from four to nine seg- 

 ments without any alleviating circumstances. The number of theories 

 seems to agree closely with the number of theorizers. Comparative 

 anatomy as a key to morphology has been so thoroughly deposed in 

 vertebrate craniology that we must regard it with great suspicion in 



Proc.N.M.vol.xxxvi— on 33 



