36 PROC. ENT. SOC. WASH., VOL. 24, NO. 2, FEB., 1922 



plant-feeders, later turning to parasitism and then again to 

 phytophagy, perhaps in a different form? 



There can be no doubt that the progenitors of the Chalci- 

 doidea at perhaps the earliest period in their developmental 

 history were plant feeders. Whether the morphological break 

 away from the ancestral type of structure which resulted in the 

 development of the modern Chalcidoidea took place before the 

 beginning of the parasitic habit, coincidental with it, or whether 

 parasitism developed after the break is an interesting problem 

 but is beside the point. Unless one is willing to believe that they 

 arose from a source entirely separate from that of other insects 

 and at a later date, it is impossible to conceive of the Chalci- 

 doids and their ancestors always having been parasitic. The 

 possibility of such an origin will, I think, be rejected without 

 serious consideration and the first stated hypothesis may, 

 therefore, be discarded. 



It is evident, then, that at some point in their evolution the 

 Chalcidoidea themselves or their ancestors were phytophagous 

 and that parasitism must have been a subsequent development. 

 The second and third hypotheses may be restated as one in the 

 following manner: Did a part of the original Chalcidoid stock 

 become adapted to a parasitic life while another part retained 

 its original plant-feeding habits, and could these two habit- 

 groups (if I may so designate them) maintaining such entirely 

 different modes of existence have come down to us through the 

 ages without any radical divergence in structure which would 

 enable us" at the present day to separate them into different 

 genera and only with great difficulty into different species? 



I believe not. The very numerous and highly specialized 

 forms to be found among the Chalcidoids seem to indicate a 

 high degree of plasticity and it would appear extremely unlikely 

 that two such different modes of existence could be main- 

 tained throughout long geological periods without resulting in 

 the development of marked structural differences to correspond. 

 One would naturally expect structural differentiation between 

 two such habit-groups if long continued and it would be much 

 easier to believe that phytophagy as found to-day is a continua- 

 tion from ancestral type if it were at present confined to a 

 restricted group or to nearly related groups. Such is apparently 

 not the case, however, as we find it showing up more or less 

 sporadically throughout the superfamily and in such widely 

 separated groups, as regard specialization of structure, as 

 Eurytomidae and Eulophidae. Acceptance of the idea that 

 phytophagy on the one hand and parasitism on the other could 

 exist for any great length of time without differentiation of 

 structure would, it seems, in an inverse manner, entail rejection 

 of the fundamental principle that environment is one of the 

 controlling factors in structural modification. Verification of 



