THE HEAD CAPSULE. 117 



b. On the Nomenclature of the Sutures and Sclerites of the Head 



Capsule. 



Before attempting a detailed description of the head capsule 

 of the Blow-fly, I shall define the terms which may be very 

 generally applied to the sutures and sclerites which are found 

 in the head capsule of an insect. 



In the Earwig, Forficula (Fig. 22), or the Cockroach, the 

 median epicranial suture will be readily recognised (Fig. 

 22, v .Y). Its anterior extremity bifurcates and marks the 

 anterior limit of the paired epicephalic sclerites. 



The diverging branches of the epicranial suture I term 

 ' epifrontal sutures ' (Fig. 22, x, y). On either side of the 

 epicranial suture a faint suture (u y f) separates the para- 

 cephalon from the median region of the head capsule. The 

 antenna is articulated either directly or through the medium 

 of a small sclerite the torulus (/) with the anterior border 

 of the paracephalon (p). 



Immediately above the antenna in Forficula, and in many 

 other insects, there is a dark spot ; it marks the junction of 

 the internal skeleton of the head with the anterior border of 

 the paracephalon. The occipital foramen is surrounded by a 

 scleritic ring the metacephalon, which consists of the dorsal 

 and lateral parts of the three first post-oral somites. 



The sternal portion of these somites forms the gula, or 

 greater part of the lower surface of the head, in the Coleoptera. 

 In the Earwig and many Orthoptera, however, the gula is ap- 

 parently internal. Although the axis of the head is more or less 

 vertical, the gula remains nearly horizontal, and is concealed 

 by the mandibles and maxillae ; under these circumstances it is 

 little developed in the middle line, but assumes the form of two 

 lateral bars, which support the mandibles and join the para- 

 cephala in front. These lateral bars are, in part at least, 

 developed from the crura of the procephalic lobes (Fig. 22, 2, g). 



The base of the labium, (Fig. 22, 4, M*"} forms with the 

 cardines of the maxillae (Fig. 22, 4, wx l ) the greater part 



82 



