ANATOMY AND PHYSIOLOGY 



43 



pairs of these legs (on abdominal segments 3, 4, 5, 6, and 10), but the rest 



vary in this respect. Thus Lagoa has seven pairs (segments 2-7 and 10) 



and Geometridae two (segments 6, and 10), 



while a few caterpillars (Tischeria, Limacodes) 



have none. Larvae of saw flies (Tenthre- 



dinidae) have seven or eight pairs of abdominal 



legs and larvae of most Panorpidae, eight pairs. 



Not a few coleopterous larvae (some Ceram- 



bycidae, Phytonomus) also have abdominal legs, 



which are incompletely developed, however, as 



compared with those of Lepidoptera. 



The legless, or apodous, condition occurs 

 frequently among larvae and always in correla- 

 tion with a sedentary mode of life; as in 

 the larvae of many Cerambycidae, almost all 

 Rhynchophora, a few Lepidoptera, all Dip- 

 tera, and all Hymenoptera except Tenthre- 

 dinidae, Siricidae, and other Terebrantia. 



Among adult insects, female scale insects are exceptional in being 

 legless. 



Walking. An adult insect, when walking, normally uses its legs in 

 two sets of three each; thus the front and hind legs of one side and the 



FIG. 63. Foot of honey 

 bee, Apis mellifera. c, c, 

 claws; p, pulvillus; / 3 -/ 5 , tarsal 

 segments. After CHESHIRE. 



FIG. 64. Caterpillar of Phlegethontius sexta. Natural size. 



middle leg of the other move forward almost simultaneously though not 

 quite, for the front leg moves a little before the middle one, which, in 

 turn, precedes the hind leg. During these movements the body is sup- 



