52 THE BEGINNINGS OF LIFE. 



that the mode of formation of the shells of animals, 

 of bone, and of other structures, may be explained 

 by a process of c molecular coalescence,' and that more 

 or less similar structures may be artificially prepared j 

 and Dr. Montgomery 1 has shown how myeline, a pe- 

 culiar organic substance, under various physical con- 

 ditions can be made to assume almost all the different 

 forms of cells at present known ; whilst in the second 

 volume of his c Principles of Biology,' Mr. Herbert 

 Spencer has handled the subject of morphological 

 development, in all its details, with that fulness and 

 philosophic grasp for which he is so distinguished. 

 The shapes of plants of their branches, leaves, flowers, 

 and cells are considered on the one hand, and those 

 of animals and of their several parts on the other ; 

 and it has been shown that very many of the pecu- 

 liarities actually met with can be fully accounted for 

 by a consideration of the nature of the incident forces 

 or physical conditions to which they have been sub- 

 jected during the progress of their growth. Indeed, 

 he goes so far as to say that c it is an inevitable 

 deduction from the persistence of force, that organic 

 forms which have been progressively evolved must 

 present just those fundamental traits of form which we 

 find them present. It cannot but be that, during the 

 intercourse between an organism and its environment, 

 equal forces, acting under equal conditions, must pro- 



1 'Proceedings of Royal Society,' 1867. 



