NO. 3 INSECT HEAD SNODGRASS I3I 



The facts are quite otherwise in the Coleoptera, for here the labium 

 retains its postoccipital connections, and its base has been drawn out 

 between the lengthened postgenal margins to form the gula. 



In certain Coleoptera the postgenal margins do become closely ap- 

 proximated (fig. 49 D), but, in such cases, the gula is compressed be- 

 tween the postgenae, and sometimes almost obliterated. The gular 

 sutures may then be partially or wholly united into a median gular 

 suture, with which are closely associated the two tentorial pits (pt, 

 pt). Intermediate stages of this condition are well shown in some 

 of the Rhyncophora, in which the head is drawn out into a " snout." 



In the Neuroptera, both larvae and adults, and in larval Trichoptera, 

 a gular plate is developed showing essentially the same structure and 

 variations of form as in the Coleoptera. The gular structure has been 

 described in various members of these orders and others in addition 

 to the Coleoptera by Crampton (1921, 1928). In the Termitidae, 

 Crampton shows, the gular region of the submentum may be very 

 much elongated, and in the soldier of Termopsis its margins become 

 united with the lengthened edges of the postgenae to fomi a typical 

 gular plate. 



The question of the derivation of the gula, the answer to which is, 

 that the gula is a part of the submental region of the labium, is not 

 to be confused with the question as to the origin of the submentum 

 itself. The various views concerning the nature of the submentum 

 have been already discussed in an earlier section of this paper (page 

 yy), and the writer will reiterate here only his own personal opinion 

 that, since the submentum in generalized insects is attached laterally 

 to the postoccipital tergal region of the head, it comprises the basal 

 parts of the second maxillary appendages, to which, however, there 

 may be added a median field of the sternum of the corresponding seg- 

 ment. If the submentum is regarded as entirely the labial sternum, 

 then the sternum becomes suspended directly from the tergum of its 

 segment, and bears the appendages — Sl condition so at variance with 

 ordinary morphological relations as to discredit the premises from 

 which it is deduced. 



VII. THE HEAD OF A CATERPILLAR 

 The caterpillars are remarkable for their standardization of struc- 

 ture. In none of the other larger groups of insects is there such uni- 

 formity in fundamental organization as in the larvae of the Lepidop- 

 tera. Some species are superficially specialized, but apparently there is 

 no " generalized " caterpillar. Ontogenetically, the caterpillars prob- 

 ably represent a stage below that of the larvae of Neuroptera, and of 



