Phylctic Parallelism in Mctamorphic Species. 519 



since nearly every primary transformation must 

 entail one or more secondary changes, and 

 secondly because, as the period of time increases, 

 more numerous parts of the body must become 

 influenced by primary transforming factors. 



A tempting theme is here also offered by 

 attempting to trace the inequality of phyletic 

 development to dissimilar external influences, and 

 by demonstrating that individual organs have as a 

 rule become modified in proportion to the diver- 

 gence in the conditions of life by which they have 

 been influenced, this action, during a given period 

 of time, having been more frequent in the case of 

 one organ than, in that of the others, or, in brief, 

 by showing the connection between the causes and 

 effects of transformation. 



It would be quite premature, however, to under- 

 take such a labour at present,, since it will be long 

 before physiology is able to account for the fine 

 distinctions shown by morphology, and further be- 

 cause we hare as yet no insight into those internal 

 adjustments of the organism which would enable us 

 a priori to deduce definite secondary changes from 

 a given primary transformation. But so long as 

 this is impossible we have no means of distinguish- 

 ing correlative changes from the primary modifica- 

 tions producing them, unless they happen "to arise 

 under our observation. 



