622 



CLASS IV. INSECTA. 



St 



FlG. 378. Posterior end of body of a Beetle 

 (Pterostichus <$) (after Stein). 8, 9 dorsal plates ; 

 8' 9' ventral plates ; St stigma ; A anus ; G 

 genital opening. 



stout piece sometimes fused with the side or under surface of 

 the thorax ; (ii) the trochanter, a minute, often triangular 

 segment; (iii) the femur ; (iv) the tibia; (v) the tarsus; this 

 may in rare cases be absent, it may also consist of but one seg- 

 ment but more usually it consists of any number of segments up 

 to five which is perhaps the commonest number (Fig. 377). The 



tarsus ends in two claws 

 (rarely in one) between 

 which very frequently 

 a lobe, the empodium or, 

 when hairy, the pulvillus, 

 projects. This may, e.g. 

 in the Diptera and Hy- 

 menoptera, attain a great 

 complexity of structure. 

 The legs of insects 

 may undergo great modifications. They may become broad 

 and thick for digging, broad and flat for swimming (Fig. 377), 

 they may develop a comb for cleaning the antennae, or hairs for 

 collecting pollen, or auditory organs as in the case of the Locus- 

 tidae (Fig. 394) and Gryllidae, or stridulating organs as in the 

 Acridiidae. Very rarely are legs absent in the imago stage. 

 The remaining segments belonging to the abdomen as a rule 

 bear no appendages. There 

 are however exceptions, the 

 larvae of the Lepidoptera 

 and of the saw-flies are 

 provided with a varying 

 number of feet in this region 

 of the body. These differ in 

 structure from the thoracic 

 limbs and are termed pro- 

 legs. Again the members of 

 the Order Thysanura bear in 

 the adult a greater or smaller 

 number of projections, 

 one pair to each segment, 



uqrinllfr lnrlrprl 

 USUaUy lOOKea 



anrl csnrnp PTYI 



ana some em- 



379 _ a Hind end of abdomen of a young 



female Locusta with the protuberances of the 

 ovipositor and the anal styles; C' and C" the in- 

 ternal and external protuberances of the penu]- 

 timate . c ,, the same of the an t ep enultimate 

 segment, b slightly older stage, c nympha ; A 



anus with anal styles (a{ter Dewitz) . 



