THE EXTERNAL ANATOMY OF INSECTS 



39 



the head and that portion of the dorsal surface that is behind the 



arms of the epicranial suture. The sclerites constituting this 



region are so closely united that they were regarded as a single 



piece by Straus-Durckheim (1828), who also included the front in 



this region, the epicranial suture being obsolete in the May beetle, 



which he used as a type. 



The vertex. — The dorsal portion of the epicranium; or, more 



specifically, that portion which is next the front and between the 



compound eyes is known as the vertex (Fig. 45, V, V). In many 



insects the vertex bears the paired ocelli. It is not a definite sclerite; 



but the term vertex is a very useful one and will doubtless be retained. 



The occiput. — ^The hind part of the dorsal surface of the head is the 



occiput. When a distinct sclerite, it is formed 



from the tergal portion of the united postgenae 



described below (Fig. 47, 0, 0). 



The genae. — The gems are the lateral portions 

 of the epicranium. Each gena, in the sense in 

 which the word was used by the older writers, 

 includes a portion of several sclerites. Like 

 vertex, however, the term is a useful one. 



The postgenae. — In many insects each gena is 

 divided by a well-marked suture. This led the 

 writer, in an earher work ('95), to restrict the 

 term gena to the part in front of the suture (Fig. 

 48, G), and to propose the term postgena for the 

 part behind the suture (Fig. 48, Pg). 

 The gula. — The gtila is a sclerite forming the ventral wall of the 



hind part of the head in certain orders of insects, 



and bearing the labium or second maxillae (Fig. 



49, Gu). In the more generalized orders, the 



sclerite corresponding to the gula does not form 



a part of the skull. The sutures forming the 



lateral boundaries of the gula are termed the 



gular sutures. 



The ocular sclerites. — In many insects each 



compound eye is situated in the axis of an 



annular sclerite; these sclerites bearing the 



compound eyes are the ocular sclerites (Fig. 50, os). 

 The antennal sclerites. — In some insects there 



is at the base of ench antenna an annular sclerite; 



these are the antennal sclerites (Fig. 50, as). The antennal sclerites 



are most distinct in the Plecoptera. 



Fig. 48. — Head and 

 neck of a cock- 

 roach. 



-Head of 

 Coryd'ilus, adult, 

 ventral aspect. 



