sex. 



THE TENTH ABDOMINAL SEGMENT. 



In the present state of our knowledge, it is very 

 difficult to say what exactly represents the tenth segment, 

 it has even been questioned whether it exists at all. 

 Zander states that he has been able to discover very little 

 of the wall of the thirteenth (tenth abdominal) segment as 

 it remains membraneous and hidden beneath the twelfth 

 (ninth abdominal) segment, being withdrawn beneath it. 

 He further concludes from a study of the development 

 within the pupa that the uncus and scaphium (my gnathos) 

 are secondary appendicles of the tenth segment. How- 

 ever, for the present I can only leave the question 

 undetermined. 



THE UNCUS. Gosse. 



Attached to the dorsal portion of the tegumen is the 

 uncus. This, in the Geometrida, is generally produced 

 in the form of a hook (Cepphis advenaria, pi. Hi), usually 

 single, but sometimes bifurcate. It is, however, subject 

 to much variation, being in some species merely a thin 

 projection (Aspilates, pi. xv.) and in others practically 

 absent (Acidalia, pi. xxi.). 



THE SOCIL Pierce. 



On either side of the base of the uncus, on the ventral 

 surface there is often a hairy pad. When this pad is 

 developed into a weakly chitinised hairy process I have 

 termed it The Socius (Hemithea, pi. i) (Wytsman Genera 

 Insectorum Hemitheinse, p. 6). 



THE GNATHOS. Pierce. 



Springing from the base of the uncus, where it is 

 hinged, there is often a free ring, enclosing the anus and, 

 if present, the subscaphium, having a central curved lip 

 generally decorated with scobinations, spines, or sqnamous 

 markings. Sometimes the parts other than the curved lip 

 are fused to the tegumen, from which, in this case, the tip 



