March, 1910 1 BrUES : PARASITIC HyMENOPTERA. 7 



table, and these groups can be quite satisfactorily compared, both 

 with each other and with recent faunae. In such a comparison, the 

 most striking fact which attracts one's attention is the predominance 

 of recent genera both in amber and at Florissant. Wheeler ('08) 

 has summarized the ratio of living to extinct genera of ants known 

 from Baltic amber and finds it to be in the proportion of 24 living 

 to II extinct genera among a total on 35. The ratio of living 

 to extinct genera of parasitic Hymenoptera in this amber has not 

 yet been thus accurately determined, but there can be no doubt that 

 it is much larger in favor of the recent ones. The same prepon- 

 derance of modern genera is characteristic of the Florissant shales 

 which have been more extensively studied, for here there are 63 

 living compared to 6 extinct genera among the parasitic families. 

 The only conclusion to be reached from these data is that such types 

 must be more conservative than the ants in the development of new 

 generic types in spite of the complicated relations which they bear 

 to their hosts. The very recent discoveries of so many most extra- 

 ordinary and unexpected adaptations in the development and etho- 

 logical relations of parasitic groups makes this still more remarkable 

 for we should naturally look for correlations between such an enor- 

 mous ethological plasticity and the morphological characters associ- 

 ated with it. It would appear that the logical conclusion to be drawn 

 from such facts is that the adaptations in habits known to exist in 

 recent species must be well fixed and were also present at least 

 in a very similar form in Oligocene and Miocene species, which 

 suggests that all attempts to trace the phylogeny of the larger 

 groups must be pushed far into pre-Tertiary time. This same con- 

 clusion has been reached by other students of fossil insects of the 

 more specialized orders and it seems well nigh hopeless in the 

 present state of knowledge to attempt any generalizations concern- 

 ing the phylogeny of the larger groups of Hymenoptera from pale- 

 ontological data alone. Facts bearing on the occurrence and relation- 

 ships of pre-Tertiary Hymenoptera are extremely meager, although 

 the living families and genera appear suddenly in early Tertiary 

 (Oligocene) times in nearly the same proportion as they do at 

 present. 



The most recent attempt to trace the origin of the parasitic Hy- 

 menoptera is that of Handlirsch ('08) who falls back mainly on pale- 



