lO MARINE BIOLOGICAL LABORATORY. 



workers, uniting in such intimate fellowship as to consti- 

 tute an indissoluble whole — a real conscious intelligent 

 unity — with powers so far transcending those of its 

 units that we can form no conception of the special 

 combinations from which they result, — when we con- 

 template this miracle of co-adjustments among myriads 

 of units, among these systems of units, and these sys- 

 tems of systems, we are not disposed to ridicule the 

 judgment that once refused to believe that natural 

 forces could produce such wonders, and took refuge 

 from the difficulties that beset every mechanical theory 

 in the doctrine of preformation. 



If our microscopical aids have enabled us to know 

 that organisms are not simple unfoldings of pre-existing 

 structures, and have revealed the fact that every devel- 

 oping germ actually re-enacts the wonders of a new 

 creation, still it is no less an unscrutable mystery than 

 before. Indeed one must credit the preformationists 

 with having perceived and emphasized the real difficulty 

 in the way of any rational theory of generation. We 

 endeavor to meet it, by assuming, not pre-existing rudi- 

 ments, but pre-existing hereditary units ; not predelinea- 

 tions, but potentialities, of structure. Predeterminations 

 of some kind or other are a logical necessity, and so 

 there is some analogy between our position and that of 

 Bonnet, Haller, and Cuvier, and other evolutionists of 

 the old school, although we are compelled to regard the 

 process of development as one of epigenesis, as conceived 

 by Aristotle, Harvey, John Hunter, and Casper Fried- 

 rich Wolff. The difference between the two schools re- 

 duces itself to the difference between potentialities and 

 actualities ; and although the difference as understood 



