PARASITISM OP THE HYMENOPTEBA. 155 



in the perfect insects, are yet sufficiently strong to cor- 

 roborate the idea of their being related to each other; 

 for both have their larvae cruciform. But in what 

 manner, if any, the Tenthredines are connected to the 

 more typical bees, must be determined by analysis. 

 Characters founded upon any one single organ are ge- 

 nerally artificial : yet it is very remarkable that, in the 

 two typical groups of our arrangement of this order, the 

 caudal appendage performs the office of a sting, while 

 in the three aberrant divisions it assumes the functions 

 of an ovipositor. Should our theory of the primary 

 types be correct, no better characteristic of them can 

 be giveno 



(142.) Preliminary to our special treatment of the 

 habits., economy, distribution, and peculiarities of struc- 

 ture of the successive groups into which the Hymeno- 

 ptera have thus resolved themselves, we propose making 

 a few observations upon the order collectively. In the 

 first place, we may remark that sexual discrepancies are as 

 perplexing to the entomologist here, as in the other or- 

 ders, and there is as frequently a difficulty in associating 

 together the partners of a species : this is conspicuously 

 the case among the bees. In the aculeated division of 

 the Hymenoptera, there is, however, a tangible cha- 

 racter whereby the sex of the individual may be discri- 

 minated ; for the males have one joint more to the 

 antennae and the abdomen than the females. In the 

 preceding orders of which we have treated, we have had 

 occasion to observe the parasitical habits of many of 

 the species, which o^cur more or less considerably 

 throughout all insects. VHere, however, although it is 

 found very extensively amongst the Diptera also, it 

 reaches its maximum; for one group, the Ichneumonides, 

 as we here consider them, are almost exclusively para- 

 sites. The term will receive its explanation by our ex- 

 hibiting the characteristic and discriminating features 

 whereby it distinguishes itself in the several tribes in 

 which it occurs. The Ichneumonides , or, as they were 

 named by Latreille, Pupivora, from the peculiarity in*. 



