456 Notices of Memoirs — Professor Sollas's Address 



Again, animals do not all change their characters at the same 

 rate : some are stable, in spite of changing conditions, and these 

 have been cited to prove that none of the periods we look upon as 

 probable, not twenty-five, not a hundred millions of years, scarce 

 any period short of eternity, is sufficient to account for the evolution 

 of the living world. If the little tongue-shell, Lingula, has endured 

 with next to no perceptible change from the Cambrian down to the 

 present day, how long, it is sometimes inquired, would it require for 

 the evolution of the rest of the animal kingdom? The reply is 

 simple : the cases are dissimilar, and the same record which assures 

 us of the persistency of the Lingula tells us in. language equally 

 emphatic of the course of evolution which has led from the lower 

 organisms upwards to man. In recent and Pleistocene deposits the 

 relics of man are plentiful : in the latest Pliocene they have dis- 

 appeared, and we encounter the remarkable form Pithecanthropus ; 

 as we descend into the Tertiary systems the higher mammals are 

 met with, always sinking lower and lower in the scale of organiza- 

 tion as they occur deeper in the series, till in the Mesozoic deposits 

 they have entirely disappeared, and their place is taken by the 

 lower mammals, a feeble folk, offering little promise of the future 

 they were to inherit. Still lower, and even these are gone ; and in 

 the Permian we encounter reptiles and the ancestors of reptiles, 

 probably ancestors of mammals too ; then into the Carboniferous, 

 where we find amphibians, but no true reptiles ; and next into the 

 Devonian, where fish predominate, after making their earliest 

 appearance at the close of the Silurian times ; thence downwards, 

 and the vertebrata are no more found — we trace the evolution of the 

 invertebrata alone. Thus the orderly procession of organic forms 

 follows in precisely the true phylogenetic sequence : invertebrata 

 first, then vertebrates, at first fish, then amphibia, next reptiles, 

 soon after mammals, of the lowlier kinds first, of the higher later, 

 and these in increasing complexity 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 palgeontological 

 record is mere myth or is founded only on negative 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 underlying the Cambrian, these have 



