HEAD, MOUTH-PARTS, ORTHOPTERA EUPLEXOPTERA 255 



from the caudal portions by the encroachment of the antacoriae 

 and lateral ocelli. 



The vertex (v) in Blatta (figs. 1 and 13) extends on the caudal 

 and dorsal aspects from near the occipital foramen to the epi- 

 cranial arms, and is divided on the meson by the epicranial stem. 

 On the lateral aspect each half of the vertex extends cephalad 

 between the compound eye and the occipital suture to the man- 

 dibularia (mb), then dorsad to the frontogenal suture, and is 

 connected with the dorsocaudal part by a narrow area between 

 the compound eye and the antacoria. The vertex, therefore, 

 occupies nearly one-third of the surface of the head and includes 

 the compound eyes and lateral ocelli. 



The extent of the vertex depends upon the shape and size of 

 the head and the position of the epicranial suture. It reaches 

 its maximum development in Diapheromera and is much re- 

 stricted on the caudal aspect in Orchelimum and Tettix. The 

 lateral ocelli are not situated on the vertex in Mantis, Melano- 

 plus, and Tettix. A furrow with an accompanying parademe ex- 

 tends cephalodorsad from the occipital foramen on each lateral 

 half of the vertex in Mantis, Diapheromera, and Anisolabis. 

 Whether these furrows are homologous with the vertical furrows 

 found in the larvae of the Tenthredinidae and other Entomet- 

 abola is not known. 



The portion of the vertex cephalad of each compound eye is a 

 gena (g). It is restricted in Mantis and Diapheromera, ample 

 in Melanoplus and Tettix, and fused with the front in Orcheli- 

 mum and Stenopelmatus. In Anisolabis it is completely iso- 

 lated from the rest of the vertex by the cephalic encroachment 

 of the occipital suture. 



The compound eyes (ce) in Blatta are large, kidney-shaped, 

 emarginate on the mesal margin, and occupy the dorsal, lateral, 

 and caudal parts of the head. They are present in all the genera 

 studied, but vary in size, shape, and position. 



The narrow annular sclerite surrounding the periphery of each 

 compound eye is the oculata (ol). It is produced entad as a 

 ring-like plate (fig. 45). Oculatae are always present and the 

 ental rings are more or less well developed, reaching the maxi- 



