OF WASHINGTON. 329 



text the evolution of insects from a primitive wingless type, with 

 out metamorphosis, into more specialized types of winged and 

 wingless insects, with incomplete or complete metamorphosis. 



The thysanurians, or springtails, are always apterous and 

 undergo no distinct metamorphosis. 



If in this ideal sketch of the phylogeny of insects I have 

 drawn somewhat upon my imagination, instead of depending 

 always upon facts, for my conception of their development, I 

 have no apology to make ; but, on the contrary, claim it is just 

 as permissible for naturalists, as it is for philosophers to draw 

 sometimes upon their imagination in order to interpret nature 

 correctly. 



This ideal genealogical tree is given merely to illustrate the 

 origin of the Hymenoptera, and the position which I believe 

 these insects should occupy among Other orders, and I will now 

 proceed to say something about this order. 



The geological history of the Hymenoptera is very meagre. 

 Some authorities, and especially Mr. Samuel H. Scudder, of Cam 

 bridge, Mass., our highest authority on fossil insects, consider 

 that hexapodous insects were not ordinarily differentiated until 

 post-palaeozoic time, and class all fossil insects before this time in 

 a single order, termed Palaeodictyoptera, since these fossils cannot 

 be referable to any of our modern orders. 



Most of these insects, however, show neuropterous and or- 

 thopterous affinities and demonstrate the great age of these insects. 

 As we ascend the geological strata, insects become better differ 

 entiated and other orders appear the Hemiptera, Coleoptera, etc., 

 but no trace of hymenopterous insects appears until the tertiary 

 formation is reached. 



The earliest known fossil Hymenoptera occur in England in 

 the middle Oolite, while in this country they have been obtained 

 from different localities in the tertiary formation. Scudder in 

 his Tertiary Insects of North America (U. S. Geol. Surv., 1890) 

 describes 15 fossil terebrants and 8 aculeates from the Floris 

 sant beds of Colorado. 



These fossils, however, are of so recent a date that, with one 

 or two exceptions, all are referred to modern genera, and all 

 belong to well-defined modern families, so that no clew as to the 



