GEOLOGICAL HISTORY OF INSECTS. :;.">."> 



In attempting some years ago, in a paper already referred to, to answer this question in 

 a broad way, I stated that all the orders of Heterometabola, and none of Metabola, had been 

 found in paleozoic deposits. To-day I shall have to modify this ■proposition. Not only 

 have numerous discoveries been made in paleozoic deposits within the past six years, but 

 those already known have been subjected to more rigorous study and wider comparisons, 

 which have considerably enlarged our knowledge. Protophasma had then only just been 

 discovered, an insect which has done more than any other, excepting Eugereon, to throw 

 light on the fundamental characteristics of the early world of insects; and even now 

 Brongniart has published but five or six examples of the treasures of Commentry, a place 

 which has already yielded remains exceeding in numbers those of all the rest of the world 

 put together. Nor must we leave out of sight his discovery of a winged insect in the 

 Silurian. 



While our knowledge of paleozoic insects is thus shown to be clearly still in its infancy, 

 it may appear hazardous to attempt to formulate statements of a broad and sweeping 

 character concerning the appearance of the primary groups of insects in paleozoic times, 

 especially if 1 am already compelled within six years to modify such assertions then made. 

 Yet when I point out the nature of this modification, made after a special study of every 

 known paleozoic form, it will appear less hazardous. 



The modification I would introduce is to this effect: That while we may recognize in 

 the paleozoic i*ocks insects which were plainly precursors of existing Heterometabola, viz.: 

 Orthoptera, Neuroptera (both Neuroptera proper and Pseudoneuroptera), Hemiptera (both 

 Hoinoptera and Heteroptera), and perhaps Coleoptera — and no Metabola whatever — a 

 statement almost identical with that previously made, we may yet not call these Orthoptera, 

 Neuroptera, etc., since ordinal features were not then differentiated ; but all paleozoic 

 insects belonged to a single order which, enlarging its scope as outlined by Goldenberg, 

 we may call Palaeodictyoptera; in other words, the paleozoic insect was a generalized 

 Hexapod, or more particularly a generalized Heterometabolon. Ordinal differentiation had 

 not begun in paleozoic times. 



It will be asked, were there then no cockroaches in paleozoic times ? I answer, yes ; 

 cockroaches but no Orthoptera; Palaeoblattariae, not Blattariae ; that is, Palaeodictyo- 

 ptera, not Orthoptera. Mayflies; but they were Palephemeridae, not Ephemeridae — again, 

 not Neuroptera but Palaeodictyoptera. Walking sticks; but no Phasmida — only Protophas- 

 mida, another group of Palaeodictyoptera. 



The grounds for this view are as follows: 1. No group of paleozoic insects has yet 

 been studied carefully — and it is important to observe that, though our knowledge of 

 them is of necessity fragmentary, yet the more perfectly they are known the clearer is 

 this true — no group, I say, has been carefully studied which does not show, between it 

 and the modern group which it most resembles, differences so great that it must be 

 separated from that group as a whole, as one of equal taxonomic rank, as in the case of 

 the three related groups last mentioned. 



2. That the different larger groups of paleozoic times, of which we now know nine or 

 ten, were more closely related to one another, at least in the structure of their wings 

 (which is the only point of general structure yet open for comparison), than any one of 

 them is to that modern group to which it is most allied, and of which it was with little 



