76 PR I MAR Y FA CTORS OF ORGANIC E VOL UTION. 



of fission, but by spores, which are borne together in 

 a mass, or in a sporangium distinguished from the rest 

 of the body. A distinction between the lower animals 

 and plants is that the former introduce their food at a 

 definite, though it may be a variable, point of the body; 

 while plants absorb their nutriment in solution at all 

 points. It is however demonstrated that some animals 

 (many parasites) nourish themselves in the same man- 

 ner as do plants ; and in their early stages the Myxo- 

 mycetes have the feeding habit of the lowest animals 

 (Amoebae). Both animals and plants from a morpho- 

 logical point of view have a common origin, in a nucle- 

 ated, undivided, more or less globular piece of proto- 

 plasm or sarcode. 



From freely moving Protophyta of this form, the 

 vegetable kingdom took its rise. They first of all as- 

 sumed a sessile position on the earth, and became 

 what one may call earth-parasites. This abandonment 

 of free mobility we cannot hesitate to regard as the 

 efficient cause of a degenerate line of evolution. There 

 can be no doubt about this, since fixity of habitat at once 

 limits enormously the range of active influences which 

 tend to modify an organism, whether they proceed 

 from within it or from without it. The subsequent 

 inclosure of the protoplasm in a structure of cellulose 

 removes them from many of the stimuli which have so 

 potent an influence in the life-history of animals, and 

 the storage of other substances, as proteids, gums, 

 resins, etc., in their cells, still further emphasizes the 

 distinction. 



From this beginning, progress in plants is seen 

 chiefly in the modifications of their methods of repro- 

 duction. This function is the aim of the vegetable 

 kingdom so far as their own condition is concerned. 



