Paleocampa, Meek and Worthen. 295 
question. It would certainly be reasonable to consider the 
Archipolypoda as the common ancestors of both the Chilopoda 
and Diplopoda—and possibly the Protosyngnatha as the 
descendants on one line of a primitive type which, on another 
line, has retained its integrity up to the present day in Per?- 
patus (and on possibly a third line has reached Scolopendrella), 
while on that which produced Palceocampa it has not, so far 
as we know, survived the Carboniferous epoch. With the 
facts of structure of ancient and modern types now before us, 
we are compelled, on any genetic theory, either to presume a 
great acceleration of development in earlier times or to look 
for the first appearance of myriopods at a vastly remoter epoch 
than we have any reason to do from the slighter hints in the 
_ rocks themselves—a period so remote as to antedate that of 
winged insects, which are now known from rocks older than 
any which have yielded remains of myriopods. In a memoir 
on Devonian insects, the concluding portion of which was re- 
published in this Journal *, I showed the probability, on de- 
velopmental grounds, that some of the Carboniferous insects, 
“together with most of those of the Devonian, descended 
from a common stock in the Lower Devonian or Silurian 
period, and that the union of these with the Paleodictyo- 
ptera (of the Carboniferous) was even further removed from 
us in time.” The structural relations of myriopods and hexa- 
pods render it probable that the former preceded the latter ; 
and in complete accordance with this expectation, the struc- 
tural relations of the oldest fossil myriopods indicate their 
apparition at a period earlier than that to which the winged 
insects are hypothetically assigned. This would compel us 
to consider the earlier type as aquatic, for which we have 
presumptive evidence in the structure of the Huphoberide, 
and renders i+ all the more surprising that the penetrating re- 
searches of the last thirty-seven years, since the first Carbo- 
niferous myriopod was discovered, have not yielded the 
slightest trace of fossil myriopods below the Coal-measures, 
This discrepancy between fact and hypothesis should never 
be lost sight of, and should stimulate to more searching inves- 
tigations, particularly of those articulates of the older rocks 
whose aflinities have not been satisfactorily settled. 
* Am, Journ, Sci. vol. xxi. p. 117. 
