494 



HYMENOPTERA 



CHAP. 



The legs of bees exhibit modifications for industrial purposes. 

 In the stinging Hymenoptera the trochanters are usually of a 

 single piece, and these Insects are called monotrochous ; but in most 

 of the other forms the trochanters are more or less distinctly 

 divided into two parts (Fig. 345, &). The usual number of joints 

 in the tarsus is five, but is subject to diminution in many cases. 

 In the bees and ants the first joint is altered in form ; in the 

 bees to act as an instrument for gathering or carrying pollen ; in 

 the ants to act, as it were, as a second tibia. Between the 

 claws there is a very perfect pad, already described and figured 

 on p. 106. 



The wings are remarkable for the beautiful manner in which 



the hinder one is united to the 

 anterior, so that the two act in 

 flight as a single organ. The 

 hind wing is furnished with a 

 series of hooks, and the hind 

 margin of the front wing is 

 curled over so that the hooks 

 catch on to it. In some of the 

 parasitic forms the wings are 

 almost destitute of nervures, 

 and have no hooks. The powers 

 of flight in these cases are prob- 

 ably but small, the wings merely 

 serving to float the Insect in 

 the air. In some Hymenoptera, 

 especially in Pompilides and 

 Xylocopa, the wings may be 

 deeply pigmented or even me- 

 tallic ; and in some forms of 

 Ichneumonidae, 

 the pigmenta- 



'Fio. 337. Wings of a carpenter bee. A, 

 The pair of wings separated ; a, posi- 

 tion of the hooks : B, the same wings 

 when united by the hooks. C, Portions 



of the two wings : a, the series of Tenthredinidac, 



hooks ; 0, marginal hairs ; c, portion of ^ -t^ . -, 



edge of front wing, of which the other and BraCOnidaC 



show\he^hook^^''' ^'''^^^ '"^ '''^^' *"" *^^^ assumes the form of definite 



patterns. 

 The studies of the internal anatomy of Hymenoptera are at 

 present by no means numerous or extensive. The alimentary canal 

 (Fig. 69) possesses a crop, gizzard, and chylific stomach in addition 

 to the oesophagus and intestine. The social Hymenoptera have 

 the power of disgorging matter from the alimentary canal for the 



