38 PROC. ENT. SOC. WASH., VOL. 23, NO. 2, FEB., 1921 



phylogeny, the Coleoptera should be placed in the same super- 

 order with the Neuroptera, and occupy a position very close to 

 the latter insects. On the other hand, the Coleoptera are 

 extremely closely related to the De'rmaptera, as is shown by the 

 character of the maxillae, thoracic terga, "larval" cerci, and 

 other structures, so that is is extremely difficult to determine 

 whether to group the Coleoptera with the Dermaptera or with 

 the Neuroptera. At any rate, the Coleoptera are anatomically 

 intermediate between the Neuroptera and the Dermaptera, and 

 if this fact has any significance (as every morphologist would 

 claim that it does) it clearly indicates that on one side of their 

 lineage, at least, the Hymenoptera, Neuroptera and Coleop- 

 tera were descended from ancestors very like the Dermaptera, 

 and it is quite possible that the tendency toward the develop- 

 ment of symmetrical genitalia exhibited by. male Hymenoptera 

 was inherited from this side of their ancestry. 

 . While the Hymenoptera (and Neuroptera) may trace their 

 lineage through Coleoptera-like forms to ancestors resembling 

 the Dermaptera on one side of their ancestry, there is another 

 side of their lineage of even greater importance, which leads 

 back with the Psocida to ancestors resembling the Zoraptera 

 and Isoptera. The head capsule of certain Psocidae is very like 

 that of certain Hymenoptera, the wing venation in the two 

 groups offers many points of similarity, and the same is true of 

 the thoracic terga and the nature of the ovipositor. Similarly 

 the head capsule of the Zoraptera (which are like the ancestors 

 of the Psocida) is extremely like that of the lower Hymenoptera, 

 the thoracic terga and wings exhibit many points of resemblance 

 in the two groups, and the cerci (among other features of the 

 terminal abdominal structures) are very much alike in the 

 Hymenoptera and Zoraptera. In fact, it is quite probable that 

 the inherent tendency toward the development of social life 

 exhibited by the Zoraptera (and to a greater extent by their 

 near relatives, the Isoptera) has passed on to the Hymenoptera 

 from this source. 



Thus, when we take into consideration a greater number of 

 anatomical, developmental, and biological features, and also 

 take into consideration the points of convergence of the lines 

 of development on either side of the Hymenoptera as well, it 

 becomes apparent that the line of development of the Hymenop- 

 tera, together with that of the Psocida and the Neuroptera, etc., 

 leads back to ancestors resembling the Dermaptera (with the 

 Coleoptera) on the one side, and the Isoptera (with the Zorap- 

 tera) on the other. Since the mutual resemblances which one 

 finds in the groups in question would be inexplicable under any 

 other view, and since all of the known facts are in perfect agree- 

 ment with this view, there can be but little doubt that it is the 

 correct one. 



