12 MORPHOLOGICAL DEVELOPMENT. 



it must have been structurelesss ; since, as differentiations are 

 producible only by the unlike actions of incident forces, there 

 could have been no differentiations before such forces had had 

 time to work. Hence, distinctions of parts like those required 

 to constitute a cell, were necessarily absent at first. And we 

 need not therefore be surprised to find, as we do find, specks 

 of protoplasm manifesting life, and yet showing no signs of 

 organization. A further stage of evolution is 



reached, when the very imperfectly integrated molecules form- 

 ing one of these minute aggregates, become more coherent ; 

 at the same time as they pass into a state of heterogeneity, 

 gradually increasing in its definiteness. That is to say, we 

 may look for the assumption by them, of some distinctions of 

 parts, such as we find in cells, and in what are called uni- 

 cellular organisms. They cannot retain their primordial uni- 

 formity ; and while in a few cases they may depart from it 

 but slightly, they will, in the great majority of cases, acquire 

 a very decided multiformity there will result the compara- 

 tively integrated and comparatively differentiated Protophyta 

 and Protozoa. The production of minute aggregates 



of physiological units, being the first step ; and the passage of 

 such minute aggregates into more consolidated and more 

 complex forms, being the second step ; it must naturally hap- 

 pen that all higher organic types, subsequently arising by 

 further integrations and differentiations, will everywhere bear 

 the impress of this earliest phase of evolution. From the 

 law of heredity, considered as extending to the entire succes- 

 sion of living things during the Earth's past history, it 

 follows, that since the formation of these small, simple organ- 

 isms, must have preceded the formation of larger and more 

 complex organisms, the larger and more complex organisms 

 must inherit their essential characters. We may anticipate 

 that the multiplication and combination of these minute 

 aggregates or cells, will be conspicuous in the early develop- 

 mental stages of plants and animals ; and that through- 

 out all subsequent stages, cell-production and cell-differen 



