76 THE COCKROACH [CH. Ill 



wide of the entrance by the whole leg so soon as the insect 

 is well clear of the tunnel. 



The third and fourth joints of the legs (femur and tibia), 

 especially the latter, have upon their surfaces numerous 

 stiff projecting bristles whose use is at once evident if 

 dust or any fine powder is thrown over the insect. The 

 foreign matter is without delay removed ; the antennae are 

 drawn repeatedly through the closed mandibles and wiped 

 clean, and then the legs are called into play and used as 

 brushes or combs to scrape every part of the body, the 

 tibial bristles being chiefly utilised in this work of 

 cleansing. From time to time the legs themselves are 

 relieved of their load of dirt either by the two members 

 of a pair being rubbed together, or by one leg being drawn 

 between two others closely approximated, or, again, by the 

 action of the mandibles. It will be noticed that all the 

 bristles point towards the apex of the leg and so foreign 

 matter caught by them is inevitably driven towards the 

 claws and is thus cleared away by any friction of the leg. 



The cleansing contrivances of insects are variously 

 situated and of varying degrees of perfection. Common 

 house-flies are often seen diligently cleaning their wings 

 and bodies by a series of brushing movements of the legs, 

 followed by rubbing the legs together and thus casting 

 away the collected dirt. In their case there is a more 

 definitely specialised brush ; the bristles on the leg are 

 far finer and more closely set, and, in the absence of 

 suitable mandibles, the legs are obliged to free each other 

 of the dust collected. In some insects there are situated 



