CLASSIFICATION. 15 



proposed to divide the Hymenoptera into Ditrocha and Mono- 

 trocha, in accordance with the number of joints in tlieir trochanter ; 

 but here difficulties arose, since no hard and fast line could be 

 dra\\n, instances occuri'ing in which a second joint was distinctly 

 present though connate with, and apparently forming jDart of, 

 tlie femur ; and the ensuing divisions separated forms having 

 obviously natural affinities and gave rise to the most incongruous 

 grouping of species. Ashmead primarily divides the Hymenoptera 

 into Phytophaga, in which the abdomen is sessile, with the 

 tiochauters two-jointed, and tlie larva? possess legs ; and Hetero- 

 phaga, iu which the abdomen is more or less petiolate, with the 

 troelianters either one- or two-jointed, and the larvse are apodous. 

 The latter is further split up into the Aculeata, with the Oxyura 

 or Proctotrypidse, emitting the terebra from the apex of the 

 abdomen ; and the Ichueumonoidea, with the Cynipoidea and 

 Chalcidoidea, emitting the terebra from the ventral surface of the 

 abdomen. But further evidence is, I think, still needed before 

 mingling the heterogeneous Proctotrypidas A\'ith the Aculeata, 

 though Konow has fully demonstrated the affinity of the Chrysi- 

 dida3 with the latter. 



The above in reality diifers but little from A\^est\\'ood's classi- 

 fication, though it raises the Phytophaga to equality with the 

 Entomophaga and Aculeata, which latter Bingham regarded as 

 collectively constituting the Petiolata. But modern authors are 

 becoming unanimous that there should be not a dichotomous but 

 a three-fold classification, in which each section possesses some 

 feature common to the remaining two ; and the ancestral type of 

 venation is somewhat hypothetical. The first of these sections is 

 the Vespoidea, bearing one-jointed trochanters, petiolated abdomen, 

 and in the ancestral type four cubital cells. The second is the 

 Ichueumonoidea, bearing two-jointed trochanters, petiolated abdo- 

 men and but three (often supposititious) cubital cells. The third 

 is the Tenthredinoidea, bearing two-jointed trochanters, sessile 

 abdomen and four cubital cells. Thus we have the first and 

 second sections constituting the Clistogaster ; the third the 

 Chalastogaster ; the second and third the Ditrocha ; the first the 

 Monotrocha ; the first and third the Tetrastega ; and the second 

 the Tristega. I am certainly of the opinion that the distinctions 

 between the Phytophaga or sawflies, the Entomophaga or Ichneu- 

 mons in general, and the Aculeata are too natural and nowadays 

 well-known to need further elucidation. It is with the second 

 division alone that we are concerned. 



