November 23, 1900.] 



SCIENCE. 



789 



sion of organic forms follows in precisely 

 the true phylogenetic sequence; inverte- 

 brata first, then vertebrata, at first fish, 

 then amphibia, next reptiles, soon after 

 mammals, of the lowlier kinds first, of the 

 higher later, and these in increasing com- 

 plexity of structure till we finally arrive at 

 man himself. While the living world was 

 thus unfolding into new and nobler forms, 

 the immutable Lingula simply perpetuated 

 its kind. To select it, or other species 

 equally sluggish, as the sole measure of the 

 rate of biologic change would seem as 

 strange a proceeding as to confound the 

 swiftness of a river with the stagnation of 

 the pools that lie beside its banks. It is 

 occasionally objected that the story we 

 have drawn from the paleontological record 

 is mere myth or is founded only on nega- 

 tive evidence. Cavils of this kind prove a 

 double misapprehension, partly as to the 

 facts, partly as to the value of negative 

 evidence, which may be as good in its way 

 as any other kind of evidence. 



Geologists are not unaware of the pitfalls 

 which beset negative evidence, and they do 

 not conclude from the absence of fossils in 

 the rocks which underlie the Cambrian that 

 pre-Cambrian periods were devoid of life; on 

 the contrary, they are fully persuaded that 

 the seas of those times were teeming with 

 a rich variety of invertebrate forms. How 

 is it that, with the exception of some few 

 species found in beds immediately underly- 

 ing the Cambrian, these have left behind 

 no vestige of their existence ? The expla- 

 nation does not lie in the nature of the sedi- 

 ments, which are not unfitted for the preser- 

 vation of fossils, nor in the composition of 

 the then existing sea water, which may 

 have contained quite as much calcium car- 

 bonate as occurs in our present oceans ; and 

 the only plausible supposition would appear 

 to be that the organisms of that time had 

 not passed beyond the stage now repre- 

 sented by the larvae of existing invertebrata. 



and consequently were either unprovided 

 with skeletons, or at all events with skele- 

 tons durable enough for preservation. If 

 so, the history of the earlier stages of the 

 evolution of the invertebrata will receive 

 no light from paleontology and no direct 

 answer can be expected to the question 

 whether, eighteen or nineteen millions of 

 years being taken as sufficient for the evo- 

 lution of the vertebrata, the remaining 

 available eight millions would provide for 

 that of the invertebrate classes which are 

 represented in the lowest Cambrian deposits. 

 On (i, priori grounds there would appear to 

 be no reason why it should not. If two mil- 

 lions of years afforded time enough for the 

 conversion of fish into amphibians, a similar 

 period should suffice for the evolution of 

 trilobites from annelids, or of annelids 

 from trochospheres. The step from gastru- 

 las to trochosphei'es might be accomplished 

 in another two millions, and two millions 

 more would take us from gastrulas through 

 morulas to protozoa. 



As things stand, biologists can have 

 nothing to say either for or against such a 

 conclusion ; they are not at present in a 

 position to offer independent evidence ; nor 

 can they hope to be so until they have 

 vastly extended those promising investiga- 

 tions which they are only now beginning to 

 make into the rate of the variation of spe- 

 cies. 



TJNEXPEOTBD ABSENCE OP THERMAL META- 

 MORPHOSIS IN ANCIENT BOOKS. 



Two difficulties now remain for discus- 

 sion : one based on theories of mountain 

 chains, the other on the unaltered state of 

 some ancient sediments. The latter may 

 be taken first. Professor van Hise writes 

 as follows regarding the pre-Cambrian 

 rocks of the Lake Superior district : " The 

 Penokee series furnishes- an instructive les- 

 son as to the depth to which rocks may be 

 buried and yet remain but slightly affected 



