18 



There are two sclerites on each side of the head in this segment, one on each 

 side of the invagination, but the cephalic one is so reduced that it can be rec- 

 ognized only with difficulty. 



The articulation of one of the lateral cervical sclerites with 

 the maxillary segment. 



Make a drawing of the lateral aspect of the head showing 

 the features mentioned above. 



THE MOUTH-PARTS OF THE COCKROACH. 



In the cockroach the mouth-parts are very similar to those 

 of the locust with an interesting and important difference in 

 the labium. With the named drawings of the mouth-parts of 

 the locust as guide, the parts of the mouth of the cockroach 

 can be readily determined ; the following brief notes provide 

 additional aid. 



Labrum. — Attached to the margin of the clypeus as a 

 movable cuticular flap, is the subquadrangular labrum or 

 upper lip, serving as the dorsal or anterior covering of the 

 mouth. Although the position and use of the labrum makes 

 it one of the mouth-parts, it is morphologically different from 

 the other mouth-parts in not being a modified appendage. 



Epipharynx. — The epipharynx of all insects is a continu- 

 ation or outgrowth of the upper membranous wall of the 

 pharynx. It is, in the cockroach, as in most insects with 

 biting mouth-parts, simply the ventral or internal membra- 

 nous wall of the labrum. 



- A sinall distal portion of the labrum of the cockroach is 

 rather plainly set off from the rest of tl?e labrum by a trans- 

 versal suture ; it may be that this distal part is a prolonga- 

 tion of the epipharynx alone (a condition observable among 

 certain other insects). When the labrum and epipharynx are 

 indistinguishably fused the single organ is sometimes called 

 labriim-epipharymx. 



