254 



OUR HOUSEHOLD INSECTS 



the ordinary flies, which are furnished with the latter 

 only. 



In the structure and arrangement of their organs of 

 sense, again, fleas justify our statement that they are 

 zoological oddities. While the eyes of flies are com- 

 pound, each mass often containing thousands of facets, 

 those of fleas are simple, and consist only of one rounded 

 knob on each side; and as most of the insect's preda- 

 tory operations are carried on in either partial or total 

 darkness, it would seem that even these numerically 

 reduced .visual organs are of no great avail in the 

 obtaining of food. The eyes are placed in the front of 

 a hollow space, in the hinder part of which the an- 

 tennae are lodged; these are short, 

 curiously shaped organs, and are 

 so obscurely situated that they 

 would certainly escape notice un- 

 less carefully looked for (Fig. 79). 

 The hollow in which they lie is 

 partially covered by an extension 

 of the chitinous integument of 

 the head, and the part still left 

 open is further protected at a 

 lower level by a membranous flap, 

 which can be pushed aside when 



the antennae are protruded. Their 

 FIG. 79. Antenna of Dog's 

 Flea (Puiex canis). After extraordinary shape, as well as 



their concealed and guarded posi- 

 tion, indicates that many interesting problems await 

 solution as to their functions and the particular uses of 

 the several parts. 



The last two thoracic segments carry a rounded scale 

 on each side, projecting from their hinder edge. The 

 first is a minute one, but the second very much larger, 



