20 



Mandibular palp. 



Maxilla;. 



2nd Maxilla;. 



Labial palps. 



many smaller divisions ; it is quite transparent and therefore easily 

 overlooked. Two chitinous hairs of the ordinary kind arise from the 

 outer proximal surface, and a little farther up another hair of quite a 

 different character is found. It is quite transparent, gracefully curving 

 outwards towards the end, which is rounded and not pointed as is 

 usual with hairs. Possibly this is the rudiment of the mandihular palp 

 as seen in Crustacea. 



Next to the mandibles come the first pair of maxillae. These are 

 very transparent and consequently difficult to see. Each maxilla 

 (fig. 7) is seen to consist of a large rounded base and two short 

 segments, the last being covered with minute papillae. The base bears 

 three minute hairs externally, and internally a long somewhat chitinous 

 chelate claw. The two claws lie horizontally and are partly hidden by 

 the deeply chitinous submentum. They almost meet in the middle 

 line, and as they are capable of slight movement it seems probable that 

 they are concerned with the guidance of the silk threads as they pass 

 out of the mouth. 



The second pair of maxillae unite to form the labium. This is 

 composed, as is usual in these insects, of two parts, a slightly chitinized 

 mentum and an intensely chitinized submentum (fig. jl}. The sub- 

 mentum forms the floor of the mouth and is fused with the ventral 

 portion of the epicranial plates. The anterior edge is armed with a 

 row of strong teeth, five lateral on each side, and a large five-pointed 

 tooth in the middle. The fusion of the two maxillae is incomplete 

 behind, and it is not difficult to separate them entirely by pressure. 

 Beneath the submentum and entirely hidden by it in front lies the 

 mentum; the. posterior handle-like portion projects backward beyond 

 the submentum and can be easily seen. It is capable of considerable 

 movement. Two portions may be distinguished, an anterior transparent 

 part dotted with minute papillae, and fringed with very fine hairs ; and 

 a posterior part, partly chitinous and looking like a handle (fig. jn and 

 fig. 16). 



The labial palps lie on each side of the submentum, and are fused 

 to the epicranial plates. They are known in Chironomus as the striated 



