528 PROCEEDiyaS of the XATIOXAL MUPEUM. vol. xxxvi. 



the anterior part of the mesothorax. The pseudonotum (PX) is also 

 usually hidden on account of its projecting downward before the 

 metathorax. It can easily be shown, however, by removing the 

 mesotergum from the surrounding parts (163, 170). 



The metanotum in both the Di])tera and Hymenoptera is reduced 

 in size and the subdivisions are not well marked (174, 1G9). The 

 metapseudonotum is present in both orders but is generally very 

 narrow in the Diptera. In the Hymenoi:)tera it is usuall}^ a large 

 plate (ICO, 169, PN^) continuously fused on the sides with the meta- 

 epimera (A^//;//.,), though in some cases it is narrow and scarcely 

 distinguishable from the metanotum (164). 



In the Hymenoptera there occurs a fusion of the first abdominal 

 segment with the metathorax. This fact has led to a great deal of 

 discussion among entomologists and to the production of an immense 

 amount of literature. Latreille (1821) first described the rear part 

 of the apparent Hymenopteran thorax as being a part of the abdo- 

 men and named it the "segment mediaire.*' Newman later (1833) 

 called it the " propodeon." Packard (1866), by a study of the devel- 

 opment of Bomhus^ proved that the first abdominal segment is 

 actually transferred to and becomes consolidated with the meta- 

 thorax. A great man}^ other writers have written a great many 

 opinions about it and about the opinions of other writers, and (xosch 

 (1881) has furnished a voluminous historical account of all the 

 opinions of all these writers up to his time. To his Contribution 

 to the History of Entomology (1881) the reader is referred if he is 

 interested in this phase of the subject. If not, the examination of 

 a few- specimens of the insects concerned will probably suffice. 



The abdomen of Chnbex (166) shows clearly enough that the first 

 abdominal segment (164, IT) is much more closely attached to the 

 thorax than to the rest of the abdomen. That the part in question is 

 the first abdominal segment is proved by its spiracles (/ S])) and by 

 the structure of the metathorax and of the rest of the abdomen. Tlie 

 metathorax of Cimhex (164) has, in addition to the attached part 

 {IT), its full complement of sclerites. The notum {N) and pseu- 

 donotum {PN) are present dorsall}^ and the episternum (Eps) and 

 the epimerum (Epm) laterally. In the abdomen itself, if the first 

 segment behind the one in question is counted as the first, there would 

 be present only nine segments in all, and the absurdity would be forced 

 upon us of referring the female gonapophyses to the seventh and eighth 

 segments. Hence, arguing from either end, the conclusion Avould be 

 that the median segment belongs to the abdomen. In Parasiohia 

 (160) this segment could never be regarded as more than a slightly 

 transposed part of the abdomen. However, in the higher forms, of 

 which Pepsis (160) is a good representative, the median segment is 

 so intimately grown into the metathorax that it certainly does not 



