VARIATION 



435 



of the primitive protozoan ancestors,* or that every id is con- 

 structed in accordance with the existing character of the species : 

 my real view, however, is intermediate between these two. I 

 beheve that the germ-plasm of a species always consists to a 

 great extent of specific ids, amongst which, however, some more 

 or less unmodified ancestral ones are present, the number being 

 largest when the species is young. The germ-plasm varies in 

 different species, and must differ very much in the higher and 

 lower forms ; but its transformation does not go on at the same 

 rate in all the ids, for some are modified only gradually, or are 

 transmitted unaltered through long lapses of time till they are 

 at last casually removed by a ' reducing division.'' 



This might be regarded as a defect in the process of the 

 transformation of species, for the possibility of reversion, as well 

 as the retention of inactive ancestral ids in the germ-plasm, can 

 scarcely be considered useful to the species. But in nature no 

 contrivance is absolutely perfect, — not even the marvellously 

 developed human eye : all structures are only as perfect as 

 possible^ — that is to say, as perfect as they need be in order to 

 perform their required functions. This statement also applies 

 to the mechanism for the transformation of species : — it 

 approaches perfection as nearly as is necessary for the per- 

 formance of its function. 



4. Variations on a Larger Scale 



a. The Origin of these Vai'iations 



We have till now chiefly confined our attention to the question 

 of general individual variation, as exemplified by those minor 

 hereditary differences which distinguish individuals from one 

 another. But there can be no question that variations some- 

 times occur on a larger scale, and these usually appear 

 suddenly, are met with only in single individuals, and are as a 

 rule hereditary. Darwin has given a large number of instances 

 of this kind. Although the special peculiarity of the black- 

 shouldered peacock, for example, may be due to reversion to an 

 unknown ancestral form, there are many well attested cases in 



* Compare Marcus Hartog, ' Nature,' Vol. 44, December 1891. The 

 deductions made by this autlior from my former views are logically correct, 

 but are no longer justifiable, since in the meantime I myself have gained 

 further insight into the problems concerned. 



