THE ORGANIC SUCCESSION 27 



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 disappeared, 

 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 organisation 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 iiivertebrata 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 

 palaeontological record is mere myth or is founded 

 only on negative evidence. Cavils of this kind prove 



