1917] Veracervix or Neck Region In Insects 191 



tory grafting experiment, and the mechanism for its accomplish- 

 ment in nature is utterly incomprehensible. What advantage 

 can there possibly be in rejecting the perfectly obvious, simple 

 and logical explanation of the neck plates as an intersegmental 

 region, similar in every way to the other intersegmental regions 

 of the thorax, and in the place of such a simple explanation, 

 proposing that an unparalleled and unprecedented disruption 

 and grafting experiment has taken place in the labial region 

 alone in all nature, when we know of absolutely no mechanism 

 by which such an operation could be carried out? Always, in 

 the cephalization process, both segment and appendage enter 

 into the composition of the head region, although the appendage 

 may subsequently degenerate, and the segment may become 

 indistinguishably fused with the other segments forming the 

 head capsule. 



Since the labium articulates with the head capsule, it is 

 but natural to suppose that the segment which originally 

 bore the labial appendage is included in that region of the head 

 capsule with which the labium articulates, and embryology 

 fully justifies this assumption. As is shown in Fig. 2, which 

 I have adapted from a figure of the embryological development 

 of the head of a Termite by Holmgren, 1909, the entire labial 

 segment of these insects actually enters into the composition 

 of the head capsule of the developing Termite, and does not 

 remain behind to form the neck plates, while its appendages 

 become disrupted and graft themselves upon the head capsule. 

 Furthermore, the neck plates are unusually well developed in 

 the Termites (which are quite closely related to the Blattids), 

 and if these neck plates really represent the labial segment, the 

 fact would be clearly indicated in the development of these 

 insects; whereas, on the contrary, the researches of Holmgren, 

 1909, and Heymons, 1895-1905, carried out upon a great range 

 of embryos of very primitive insects, conclusively demonstrate 

 that the labial segment enters into the composition of that 

 portion of the head capsule to which the labium is articulated, 

 and which one would naturally expect, from the manner in 

 which all other appendages are articulated to the segment 

 which originally bore them, instead of unnaturally grafting 

 themselves upon some other region ! 



On this account, I am inclined to regard as a ^'lapsus 

 calami'' the including of the neck plates in the labial segment 



