terminal segments of Aculeate Hymenoptera. 253 



modified only according to the species, but perfectly 

 distinct from those of the allied genera ; and also that, 

 in like manner, a general similarity of form will run 

 through a whole family. Certainly the adoption of these 

 characters brings genera together in accordance with 

 those derivable from general outline facies, &c., — in fact 

 gives what appears to be a natural arrangement. 



Eegarding an aculeate hymenopterous insect theoreti- 

 cally as a twenty or twenty-one segmented creature, six 

 or seven of these segments, according to which view is 

 adopted, are represented at one apex in the combination 

 which we call the head, which bears various pairs of 

 appendages denoting the existence of the segments. At 

 the other apex of the creature two segments, I believe, 

 are represented in what is called the genital armature of 

 the <? , the 9th abdominal segment beyond the basal 

 constriction, i. e., not reckoning the propodeum of New- 

 man, being represented by the *' cardo " of Thomson, 

 and its appendages by the stipites, the 10th being repre- 

 sented dorsally by the spatha, and its appendages by the 

 sagittge ; the 8th segment of the abdomen also in some 

 genera bears appendages dorsally, as if it also were 

 tending to join the combination. Now, as the shapes 

 and appendages of the head-segments are regarded as 

 amongst the best and most constant for generic classi- 

 fication, I think there is good reason why the shapes 

 of the modified segments and appendages which com- 

 pose and surround the armature should have equal 

 value. 



Of course no single character should be employed to the 

 exclusion of others, and, without extending one's obser- 

 vations to the many exotic genera which I have been 

 unable hitherto to examine, it is impossible to say how 

 far these characters will prove constant. Still, from 

 what I have been able to examine, I have little doubt 

 that they afford a good basis for classification, and that 

 the extension of one's observations would show that a 

 classification on these sexual characters would produce a 

 far more natural arrangement than the one we have at 

 present in use. 



The great difficulty to be contended with is that of 

 obtaining subjects for dissection, and I should be most 

 thankful to any one who can give me old specimens of 

 exotic aculeates, however broken, for that purpose, i.e., 

 so long as the apex of the abdomen remains. 



