EXTERNAL ANATOMY OF THE COLEOPTERA. 



23 



There are also in some few beetles two ocelli, or addi- 

 tional eyes, small, and noj; composed of facets, on the 

 back of the head ; these are especially noticeable in 

 Omalium, a genus of the Brachelytra. The antennae 

 are long flexible instruments, through which the insect 

 certainly receives a considerable amount of sensation, 

 either by actual contact or atmospheric influence. They 

 are nearly always composed of eleven joints, though 

 some of them are often indistinct, being clubbed to- 

 gether, and in a few species the absolute number varies ; 

 for instance, in the male of Ischnomera melanura there 

 are twelve joints, though the normal number is found 

 in the female. They are inserted into a cup-like socket 

 in the head, and have often the first or basal joint long, 

 and the second short ; but their variations in structure 

 are too numerous to be specified here. 



Fig. 4 shows the 

 under side of the 

 head ; , b y and c 

 forming the labium 

 or lower lip, where- 

 of a is the mentum 

 or chin, b the ligula 

 or tongue, and c c 

 the labial palpi or 

 lip feelers ; d d are 

 the maxilla or lower 

 jaws (which are 

 dissected out, and 

 show the upper and 

 under sides), com- 

 posed of the following pieces : d 1 , the inner or palpiform 

 lobe; d 2 , the maxillary palpus or jaw feeler; d 5 , the 



Fig. 4. 



D. marginalis, (highly 



