POND LIFE. 



95 



dissection. These are the upper lip or labrum, the 

 tips of the mandibles, and the lower lip or labium. 

 The maxillae are usually concealed when the mouth 

 is closed. The labium is very large and ends in 

 three broad flaps, one below the mouth and one on 

 each side ; the one below the mouth is sometimes 

 more or less split on the middle line, and each of the 

 side flaps bears a slender appendage ; sometimes, 

 however, these appendages are very minute. 



8. Study the parts of the head already examined 

 with a view to seeing how they are fitted to their 

 use. The most conspicuous parts are the very large 

 eyes ; evidently the sense of sight is exceedingly im- 

 portant to these insects ; note also that the shape of 

 the eyes is such that the insect can see in all direc- 

 tions without making any movement of the head or 

 body. Regarding the simple eyes, we can only say 

 that three well-developed ones are present ; no one 

 has yet discovered the peculiar use of these eyes as 

 distinguished from that of the compound eyes, but 

 it seems as if they must have a function different 

 from that of the compound eyes, else why should an 

 insect with such highly developed compound eyes 

 possess simple eyes also. In many insects the sense 

 of smell is believed to have its seat in the antennae ; 

 if that is so in dragon-flies, it is evident that com- 

 paratively little use is made of this sense by these in- 

 sects, for the antennae are so slightly developed as to 

 be little more than rudimentary organs ; but it is not 

 strange that insects so well provided with organs of 

 sight should have little use for organs of smell in 

 hawking their prey or in seeking their mates. The 

 mouth -parts are admirably fitted for seizing and 



