170 S. II. SnnJ,/, ,'—I)'nu ,'x'dy of Type in ancient Myriapods. 



those which separate so sharply these great modern groups. 

 Whether they are to be looked upon, one as the ancestor of 

 one, the other of the other, of these modern groups, is another 



question. It would certainly be reasonable to consider the 

 Archipolypoda as the common ancestors of both the Chil- 

 opoda and Diplopoda; and possibly on the Protosyngnatha 



as the descendants on one line ot a primitive type wnicn, 

 on another line, has retained its integrity up to the pres- 

 ent day in Peripatus (and on possibly a third line has 

 reached Scolopendrella); while on that which produced Palseo- 

 campa 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 myriapods 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 myria- 

 pods. In a memoir on Devonian insects, the concluding por- 

 tion of which was republished in this Journal,* I showed the 

 probability, on developmental grounds, that some of the Car- 

 boniferous insects, "together with most of those of the Devo- 

 nian, descended from a common stock in the Lower Devoniau 

 or Silurian period ; and that the union of these with the Palas- 

 odictyoptera (of the Carboniferous), was even further removed 

 from us in time." The structural relations of myriapods and 

 hexapods render it probable that the former preceded the lat- 

 ter: and in complete accordance with this expectation, the 

 structural relations of the oldest fossil myriapods indicate their 

 apparition at a period earlier than that to which the winged 

 insects are h\ > t e-ri a! > — igned. This would compel us to 

 consider the earlier type as aquatic, for which we have pre- 

 sumptive evidence in the structure of the Euphoberidse, and 

 renders it all the more surprising that the penetrating re- 

 searches of the last thirty-seven years, since the first Carbon- 

 iferous myriapod was discovered, have not yielded the slightest 

 trace of fossil myriapods below the Coal measures. This dis- 

 crepancy between fact and hypothesis should never be lost 

 sight of, and -hould stimulate to more searching iio 

 particularly of those articulates of the older rocks whose affin- 

 ties have not been satisfactorily settled. 



