Dr. Wallich on Siliceous Sponcje-groioth. 261 



It is quite as if we were on two distinct lines of descent when 

 we study the Devonian and the Carboniferous insects : they 

 have little in common ; and each its peculiar comprehensive 

 types. Judging from this point of view, it would be impos- 

 sible to say that the Devonian insects showed either a broader 

 synthesis or a ruder type than the Carboniferous. This, of 

 course, may be, and in all probability is, because our know- 

 ledge of the Carboniferous insects is in comparison so much 

 more extensive ; but, judging simply by the facts at hand, 

 it appears that the Carboniferous insects carry us back both 

 to the more simple and to the more generalized forms. We 

 have nothing in the Devonian so simple as Euephemerites^ 

 nothing so comprehensive as Eugereon^ nothing at once so 

 simple and comprehensive as Dictyoneura. On the derivative 

 hypothesis we must presume, from our present knowledge of 

 Devonian insects : — that the Pala^odictyoptera of the Carboni- 

 ferous are already, in that epoch, an old and persistent em- 

 bryonic type (as the living Ephemeridaj may be considered 

 today, on a narrower but more lengthened scale) ; that some 

 other insects of Carboniferous times, 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 Palaiodictyoptera was even further removed 

 from us in time, carrying back the origin of winged insects 

 to a far remoter antiquity than has ever been ascribed to them, 

 and necessitating a faith in the derivative hypothesis which 

 a study of the records preserved in the rocks could never alone 

 afford ; for no evidence can be adduced in its favour based 

 only on such investigations. The profound voids in our 

 knowledge of the earliest history of insects, to which allusion 

 was made at the close of my paper " On the Early Types of 

 Insects," are thus shown to be even greater and more obscure 

 than had been presumed. But I should hesitate to close this 

 summary without expressing the conviction that some such 

 earlier unknown comprehensive types as are indicated above 

 did exist and should be sought. 



XXIV. — On Siliceous Sponge-growth in the Cretaceous Ocean. 

 By Surgeon-Major Wallich, M.D. 



A FEW days after the publication of the '■ Annals ' for 

 February, I obtained a sight of Mr. G. J. Hinde's very in- 

 teresting little work on Fossil Sponge-spicules found in the 



