1885.] Geology and Paleontology. 877 
while we may recognize in the Palzozoic rocks insects which 
were plainly precursors of existing Heterometabola, viz., Orthop- 
tera, Neuroptera (both Neuroptera proper and Pseudoneuroptera). 
Hemiptera (both Homoptera and Heteroptera) and perhaps Col- 
eoptera—and no Metabola whatever—a statement almost identi- 
cal with that previously made, we may yet not call these Orthop- 
tera, Neuroptera, etc., since ordinal features were not differentiated ; 
but all’ Palaeozoic insects belonged to a single order which, enlarg- 
ing its scope as outlined by Goldenberg, \ we may cal Palæodic- 
tyoptera; in other words, the Palæozoic insect was a generalized 
Hexapod, or more particularly a generalized Heterometabolon. 
Ordinal differentiation had not begun in Palæozoic times. 
The grounds for this view are as follows: 
1. No group of Palæozoic insects has yet been studied care- 
fully; 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 mod- 
ern group which it most resembles, emer en so great that it 
must be separated from that group as a whole, as one of equal 
. taxonomic rank, as in the case of three felative groups last 
mentioned. 
2. That the different larger groups of Palzozoic 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 doubt, the precursor or ancestral type. 
Thus the Palæoblattariæ are more nearly allied in the ground 
structure of their wings to certain neuropteroid Palzodictyoptera 
of Palzozoic times than to the modern Blattariæ ; and yet we 
_ can so completely trace in Mesozoic times the transition from the 
Palzoblattarie to the Blattarie that no reasonable doubt can 
exist as to their descent, the one from the other. 
3. The ordinal distinction which is now found in the wing 
structure of modern insects did not exist in Paleozoic insects, 
but a common simple type of neuration which barely admitted 
of family division. 
It will appear from this that, by a sort of principle of family 
continuity, we may recognize in the Palzeozoic insects a tendency 
toward a differentiation in ordinal characters sufficient to enable 
us in an ex post facto fashion to distinguish between orthopteroid, 
neuropteroid, etc., Palaeodictyoptera. 
when we look at the insects of later formations, we find 
types of every one of the existing orders of insects—speaking of 
these orders in their broadest sense, as we have everywhere done 
in ae ema —we find every one fully developed in the Jurassic 
pe 
