THE NATURE OF THE VERACERVIX OR NECK REGION 



IN INSECTS.* 



By G. C. Crampton, Ph. D. 



Occasional references to the neck as the "labial or micro- 

 thoracic segment" in recent entomological literature indicate a 

 tendency to revive the old mistaken conception of the neck 

 region of insects as representing the labial segment, or a vesti- 

 gial segment of the thorax ("microthorax") — a view which 

 dates from the time of vStrauss-Duerkheim, 1828, and Huxley, 

 1885, but for which no real evidence has ever been adduced. 

 It is a simple matter to demonstrate (1) that the neck region 

 is in every way homologous with the other intersegmental 

 regions between the true thoracic segments, and therefore 

 cannot represent a segment at all ; (2j that like the other 

 intersegmetal regions with which it is homologous, it has no 

 ganglia or any other segmental structures, either in the adult or 

 embryonic stages; (3) that the labium is not its appendage; and 

 (4) that there is already present in the head capsule a labial 

 segment forming that portion of the head region to which the 

 labium is articulated, while the labium is not articulated to the 

 neck plates at all, the latter being formed behind the true 

 labial segment. If these facts were known, there could be no 

 excuse for arbitrarily designating the neck plates as "the 

 labial or microthoracic segment," without giving any reason 

 for justifying such a course of procedure, in the face of the 

 overwhelming evidence that the neck region does not represent 

 such a segment at all ; so that it may perhaps be worth while to 

 present the evidence which completely disproves the view that 

 the neck region is a segment either labial or "microthoracic. " 



The evidence to be adduced from comparative anatomy in 

 regard to the intersegmental nature of the neck plates, is most 

 convincing and conclusive. In Fig. 1 the intersegmental 

 plates located in the intersegmental regions designated as 

 "Int" (i. e. regions I, III and Vj are shaded so as to enable 

 one to compare them more readily in the different seg- 

 ments, the entire figure being a composite of the conditions 

 found in the most primitive of the Apterygotan and Pterygotan 



* Contribution from the Entomological Laboratory of the Massachusetts 

 Agricultural College, Amherst, Mass. 



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