702 APPENDIX D. 



and correctly reason upon, in terms of forces and motions like 

 those of sensible masses. Polarity is regarded as a resultant of 

 such forces and motions ; and when, as happens in many cares, 

 light changes the molecular structure of a crystal, and alters its 

 polarity, it does this by impressing, in conformity with mechanical 

 laws, new motions on the constituent molecules. That the reviewe r 

 should present the mechanical conception under so extremely limited 

 a form, is the more surprising to me because, at the outset of the 

 very work he reviews, I have, in various passages, based inferences 

 on those immense extensions of it which he ignores ; indicating, 

 for example, the interpretation it yields of the inorganic chemical 

 changes effected by heat, and the organic chemical changes effected 

 by light (Principles of Biology, 13). 



Premising, then, that the ordinary idea of mechanical action 

 must be greatly expanded, let us enter upon the question at issue 

 the sufficiency of the hypothesis that the structure of each organ- 

 ism is determined by the polarities of the special molecules, or 

 physiological units, peculiar to it as a species, which necessitate 

 tendencies towards special arrangements. My proposition and 

 the reviewer's criticism upon it, will be most conveniently pre- 

 sented if I quote in full a passage of his from which I have already 

 extracted some expressions. He says : 



" It will be noticed, however, that Mr. Spencer attributes the possession 

 of these ' tendencies,' or ' proclivities,' to natural inheritance from 

 ancestral organisms ; and it may be argued that he thus saves the 

 mechanist theory and his own consistency at the same time, inasmuch as 

 he derives even the 'tendencies' themselves ultimately from the environ- 

 ment. To this we reply, that Mr. Spencer, who advocates the nebular 

 hypothesis, cannot evade the admission of an absolute commencement of 

 organic life on the globe, and that the 'formative tendencies,' without 

 which he cannot explain the evolution of a single individual, could not 

 have been inherited by the first organism. Besides, by his virtual denial 

 of spontaneous generation, he denies that the first organism was evolved 

 out of the inorganic world, and thus shuts himself off from the argument 

 (otherwise plausible) that its ' tendencies ' were ultimately derived from the 

 environment." 



This assertion is already in great measure disposed of by what 

 has been said above. Holding that, though not " spontaneously 

 generated," those minute portions of protoplasm which first dis- 

 played in the feeblest degree that changeability taken to imply life, 

 were evolved, I am not debarred from the argument that the "ten- 

 dencies " of the physiological units are derived from the inherited 

 effects of environing actions. If the conception of a " first organ- 

 ism " were a necessary one, the reviewer's objection would be valid. 

 If there were an "absolute commencement" of life, a definite line 

 parting organic matter from the simplest living forms, I should be 

 placed in the predicament he describes. But as the doctrine of 

 Evolution itself tacitly negatives any such distinct separation ; and 

 as the negation is the more confirmed by the facts the more we 



