GREAT STEPS IN ORGANIC EVOLUTION 847 



organism — a step along the vegetative line — might readily arise by 

 a firm membrane being formed around the globule of chromatin. 

 A cytoplasmic matrix might be added, and the enclosed chromatin 

 bodies might increase in number and assume various shapes and 

 arrangements. 



A step in a different direction — towards a predatory or animal 

 mode of life — may have been made by the formation — round a 

 biococcus, or around several biococci — of an enveloping matrix of 

 changeful protoplasm (or periplasm) with streaming movements, 

 amoeboid outflowings, and included vacuoles. "Thus arose in the 

 beginning the brand of Cain, the prototype of the animal — that is 

 to say, a class of organism which was no longer able to build up its 

 substance from inorganic materials in the former peaceful manner, 

 but which nourished itself by capturing, devouring, and digesting 

 other living organisms. The streaming movements of the periplasm 

 enabled it to flow round and engulf other creatures; the vacuole- 

 formation in the periplasm enabled it to digest and absorb the 

 substance of its prey by the help of ferments secreted by the biococci. 

 By means of these ferments the ingested organisms were killed and 

 utilised as food, their substance being first broken down into simpler 

 chemical constituents and then built up again into the protein- 

 substances composing the body of the captor." 



A further step towards a true cell consisted in the multiplication 

 of the enclosed biococci so as to form numerous chromatin grains 

 scattered through the protoplasm. Some living Protozoa show this 

 "cytodal" phase as a transient chapter in their life-history. 



The next stage in evolution was the organisation of the chromatin- 

 grains (biococci) into a definite cell-nucleus, a complex microcosm 

 with a framework (of linin) supporting variously disposed chromatin 

 constituents. While most of the chromatin grains became aggregated 

 to form a nucleus, others remained as scattered "chromidia" in the 

 protoplasm. This was the first true cell, and the starting-point of 

 many lines of further evolution. 



Prof. Minchin's theory is vivid and some of the steps assumed 

 have their counterparts in what goes on to-day, e.g. the condensation 

 of scattered chromatin grains to form a secondary nucleus. It seems 

 difficult, however, to think of the primitive organisms as specks of 

 chromatin, seeing that chromatin is an exceedingly complex protein 

 substance. It thus seems more in line with evolutionary speculation 

 to think of a blend of simpler proteins forming a unit of protoplasm. 

 Yet it must be remembered that there is no proof that the general 

 cytoplasm of a cell, or of a Protozoon, can form digestive ferments 

 without the co-operation of chromatin. 



Another theory that is certainly interesting has been propounded 

 by Mereschkowsky. It assumes a double origin for orgcinisms, which 

 are supposed to have arisen from a combination of two quite different 



