1912] Muir and Kcrshaio — Development of 31 out h parts in Homoptcra 85 



pulled out flat with the rest of the clypeal region. The whole of 

 this part is thus one piece and undivided. 



The mandibular sulci (Fig. 12, mdc) start somewhat below the 

 antennae, extending in a curved line to the articulation of the man- 

 dibles where they meet the maxillary sulci at the base and inner 

 side of the maxillary plates. From the point of articulation of 

 the mandibles to the anterior end of the mandibular sulci, the 



mxf LC 



12a. Vertical median section through head of Plata. 

 12b. Hind view of skeleton of head of Plata. 



bottoms of the sulci are chitinized to form the mandibular pillars. 

 0\\ang to the delicacy of the rest of the sulcal membrane the man- 

 dibular pillars appear as rods projecting from the clypeal region, 

 to which the mandibles are articulated. The thinning of this 

 intermediate part of the sulci allows of a freer movement of the 



