in] MOUTH-PARTS AND SENSE-ORGANS 49 



sexes come together, the antennae of the male are 

 usually raised and exposed from the groove. Insects 

 generally have some means of cleansing dirt from 

 their antennae. Some make use of their legs, others 

 of their mouth-parts. In fleas there is often a row of 

 short hairs at the hind margin of the groove which 

 may serve as a kind of comb for cleaning these 

 delicate organs of sense. But further observation on 

 this point would be interesting, for no one appears to 

 have seen the comb in actual use. Female fleas are 

 said usually to carry their antennae esconced in the 

 grooves, whilst the males more frequently protrude 

 theirs. The antennae of the males are generally 

 longer than those of the females. 



There are certain noteworthy organs of sense 

 which appear to exist on the upper surface of a flea's 

 head and body. They take the form of small con- 

 vexities of the body surface, lentil-shaped and each 

 surrounded at the base by a ring. Somewhat similar 

 sense-organs are widely spread through the insect 

 world. As to their function, divergent views are 

 held. Some think that they are for the perception 

 of sounds, some for the perception of light rays, some 

 for the perception of rays of which we are un- 

 conscious. Since these organs are placed, at times, 

 in unprominent parts of the body it seems more 

 probable that they are affected by sound than by 

 light. 



R. F. 4 



