CH. Ill] THE COCKROACH 79 



specialised cleaning hairs. Here they are used as in other 

 insects for removing foreign substances from the surface 

 of the body, but in this case the extraneous matter is 

 retained upon the legs, and the hairs are not only much 

 longer but are beautifully branched, and thus entangle and 

 hold the pollen more securely. The subsequent removal 

 of the pollen by the mandibles is but a repetition of the 

 modus operandi already mentioned in speaking of the 

 cockroach. Nor is it difficult to imagine how the habits 

 and structural modifications of the bees may have been 

 evolved from those of more lowly but still punctiliously 

 clean ancestors. Other insects put the bristles to different 

 uses. For instance, among the Diptera or two-winged flies 

 we find the bristles of the male Platychirus modified upon 

 the tibiae and tarsi so as to form adhesive pads employed 

 in holding the female. In Tachydromia arrogans they 

 assist in grasping the prey, while in Dolichopus they form 

 so fine a down that the air is entangled in them and the 

 insect enabled to glide unwetted upon the surface of water. 

 To return to the legs of the cockroach. Beneath the 

 joints of the tarsus are soft white patches, resembling 

 velvet, which prevent slipping and give the animal a 

 foothold when running on smooth surfaces; the terminal 

 joint carries two sharply curved claws which render loco- 

 motion possible on rough vertical surfaces, and between 

 the claws is a pad, the pulvillus. Many insects, such as 

 flies, are able to walk with ease on perfectly smooth 

 vertical or even inverted surfaces. It has been found 

 that the soles of the feet (pulvilli) of such insects emit 

 minute drops of a gluey substance, which quickly hardens 



