392 THE CANADIAN NATURALIST. [Vol. ix. 



idees' by Vogt, the similarity, traced by the former between 

 certain stages in the growth of young fishes and the fossil 

 representatives of extinct members of the group, has also been 

 observed in nearly every class of the animal kingdom, and the fact 

 has become a most convenient axiom in the study of paleontol- 

 ogicai and embryological development. This parallelism, which 

 has been on the one side a strone; argument in favor of design 

 in the plan of creation, is now, with slight emendations, doing 

 duty on the other as a newly discovered article of faith in the 

 new biology. 



" But while in a general way we accept the truth of the pro- 

 position that there is a remarkable parallelism between the 

 embryonic development of a group and its paleontological history, 

 yet no one has attempted to demonstrate this or rather to show how 

 far the parallelism extends. We have up to the present time 

 been satisfied with tracinir the general coincidence, or with 



K^ CD / 



strikinc^ individual cases. 



" The resemblances between the pupa stage of some Insects 

 and of adult Crustacea, the earlier existence of the latter, and 

 the subsequent appearance of the former in paleontological 

 history, furnished one of the first and most natural illustrations 

 of this parallelism ; while theoretically the necessary development 

 of the higher tracheate insects from their early branchiate aquatic 

 ancestors seemed to form an additional link in the chain, and 

 point to the Worms, the representatives of the larval condition of 

 Insects, as a still earlier embryonic stage of the Articulates." 



Whilst stating there was hardly a class of the animal kingdom 

 which would not admit of some most interesting parallelism 

 being drawn, he remarked he had chosen for the illustration and 

 critical examination of this parallelism the limited group of 

 Sea-urchins, on account of his own familiarity with their devel- 

 opment, and with the living and extinct species. Noticing the 

 paleontological history of several families of the Echinoder- 

 mata he speaks of the Clypeastridae as follows : 



" We find there as among the Desmosticha that the earliest 

 type, Pygaster, has existed from the Trias to the present time; 

 and that, while we can readily reconstruct, on embryological 

 grounds, the modifications the earliest Desraosticha-like Echini 

 should undergo in order to assume the structural features of Py- 

 gaster, yet the early periods in which the precursors of the 

 Echinoconidse and Clypeastridse are found have thus far not 



