396 THE CANADIAN NATURALIST. [Vol. ix. 



continued to exist without interruption from the earliest epochs 

 at which they occur to the present day, would prove conclusively 

 that at any rate some groups among the marine animals of the 

 present day are the direct descendants of those of the earliest geolo- 

 gical periods. When we come to types which have not continued 

 as long, but yet which have extended through two or three great 

 periods, we must likewise accord to their latest representatives a 

 direct descent from the older." 



'• But in spite of the limits which have been assigned to this 

 general parallelism, it still remains an all-essential factor in elu- 

 cidating the history of paleontological development, and its 

 importance has but recently been fully appreciated. For, while 

 the fossil remains may give us a strong presumptive evidence 

 of the gradual passage of one type to another, we can only^ 

 imagine this modification to take place by a process similar to 

 that which brings about the modifications due to different stagfes 

 of growth, — the former taking place in what may practically be 

 considered as infinite time when compared to the short life history 

 which has given us as it were a resume of the paleontological 

 development. We may well pause to reflect that in the two 

 modes of development we find the same periods of rapid modi- 

 fications occurring at certain stages of growth or of historic 

 development, repeating in a diff'erent direction the same phases. 

 Does it then pass the limits of analogy to assume that the 

 changes we see taking place under our own eyes in a compara- 

 tively short space of time, — changes which extend from stages 

 representing perhaps the original type of the group to their most 

 complicated structures, — may, perhaps, in the larger field of 

 paleontological development, not have required the infinite time 

 we are in the habit of asking for them ? " 



