A CRITICISM ON PROF. OWEN'S THEORY. 565 



— a less yielding central axis. On the other hand, for the central 

 axis to have become firmer while remaining continuous, would have 

 entailed a stiffness incompatible with the creature's movements. 

 Hence, increasing density of the central axis necessarily went hand 

 in hand with its segmentation : for strength, ossification was re- 

 quired ; for flexibility, division into parts. The production of ver- 

 tebras resulting thus, there obviously would arise among them a 

 general likeness, due to the similarity in their mechanical condi- 

 tions, and more especially the muscular forces bearing on them. 

 And then observe, lastly, that where, as in the head, the terminal 

 position and the less space for development of muscles, entailed 

 smaller lateral bendings, the segmentation would naturally be less 

 decided, less regular, and would be lost as we approached the 

 front of the head. 



But, it may be replied, this hypothesis does not explain all the 

 facts. It does not tell us why a bone whose function in a given 

 animal requires it to be solid, is formed not of a single piece, but by 

 the coalescence of several pieces, which in other creatures are sepa- 

 rate ; it does not account for the frequent manifestations of unity 

 of plan in defiance of teleological requirements. This is quite true. 

 But it is not true, as Professor Owen argues respecting such cases, 

 that " if the principle of special adaptation fails to explain them, and 

 we reject the idea that these correspondences are manifestations of 

 some archetypal exemplar, on which it has pleased the Creator to 

 frame certain of his living creatures, there remains only the alterna- 

 tive that the organic atoms have concurred fortuitously to produce 

 such harmony." This is not the only alternative : there is another, 

 which Professor Owen has overlooked. It is a perfectly tenable 

 supposition that all higher vertebrate forms have arisen by the su- 

 perposing of adaptations upon adaptations. Either of the two anta- 

 gonist cosmogonies consists with this supposition. If, on the one 

 hand, we conceive species to have resulted from acts of special 

 creation ; then it is quite a fair assumption that to produce a higher 

 vertebrate animal, the Creator did not begin afresh, but took a 

 lower vertebrate animal, and so far modified its pre-existing parts 

 as to fit them for the new requirements ; in which case the original 

 structure would show itself through the superposed modifications. 

 If, on the other hand, we conceive species to have resulted by 

 gradual differentiations under the influence of changed conditions ; 

 then, it would manifestly follow that the higher, heterogeneous 

 forms, would bear traces of the lower and more homogeneous forms 

 from which they were evolved. 



Thus, besides finding that the hypothesis of an " ideal typical 

 vertebra " is irreconcilable with the facts, we find that the facts are 

 interpretable without gratuitous assumptions. The average com- 

 munity of form which vertebras display, is explicable as resulting 



