THE FACTORS OF OKGANIC EVOLUTION. 55 



improvement in the microscope, while it has widened our 

 knowledge of those minute forms of life described above, 

 has revealed further evidence of the fact that all the 

 larger forms of life consist of units severally allied in 

 their fundamental traits to these minute forms of life. 

 Though, as formulated by Schwann and Schleiden, the 

 cell-doctrine has undergone qualifications of statement; 

 yet the qualifications have not been such as to militate 

 against the general proposition that organisms visible to 

 the naked eye, are severally compounded of invisible 

 organisms using that word in its most comprehensive 

 sense. And then, when the development of any animal 

 is traced, it is found that having been primarily a nucleated 

 cell, and having afterwards become by spontaneous fission 

 a cluster of nucleated cells, it goes on through successive 

 stages to form out of such cells, ever multiplying and 

 modifying in various ways, the several tissues and organs 

 composing the adult. 



On the hypothesis of evolution this universal trait has to 

 be accepted not as a fact that is strange but unmeaning. 

 It has to be accepted as evidence that all the visible forms 

 of life have arisen by union of the invisible forms ; which, 

 instead of flying apart when they divided, remained 

 together. Various intermediate stages are known. Among 

 plants, those of the Volvox type show us the component pro- 

 tophytes so feebly combined that they severally carry on 

 their lives with no appreciable subordination to the life of 

 the group. And among animals, a parallel relation between 

 the lives of the units and the life of the group is shown 

 us in Uroglena and Syncrypta. From these first stages 

 upwards, may be traced through successively higher types, 

 an increasing subordination of the units to the aggregate; 

 though still a subordination leaving to them conspicuous 

 amounts of individual activity. Joining which facts with 

 the phenomena presented by the cell-multiplication and 



aggregation of every unfolding germ, naturalists are now 

 6 



