8 HERBERT SPENCER AND 



and these changes superinducing further changes, and 

 so on in ever-increasing degrees of complexity. 



Practically every author who has set out to explain 

 biological evolution in terms of the ultimate constituents 

 of organized matter, has found himself compelled to 

 assume the existence of some such units as those postulated 

 by Spencer, and there is a very general agreement as to 

 the manner in which the evolution of the animal and 

 vegetal world has proceeded from such a basis. The 

 divergence of opinion begins when the attempt is made 

 to interpret individual or, as we call it, ontogenetic 

 evolution in terms of general or phyletic evolution, and 

 when the units are used to explain the phenomena of 

 inheritance and variation. 



It is now a fact familiar to every educated person that 

 every individual organism (exception being made, for 

 the moment, of individuals propagated by buds or 

 cuttings) has its origin in a germ-cell — a minute mass 

 of the life-stuff we call protoplasm — which in its earliest 

 phase shows no further visible structure than that it is 

 composed of cytoplasm and nucleus. 



It is further well known that, normally, the co-opera- 

 tion of two such cells, one called male, the other called 

 female, is required to start those processes which lead 

 to the building up of the adult organism. But, as we 

 know of many cases in which a single germ-cell is capable 

 of procee(Jing on its course of development without the 

 co-operation of another, without being fertilized, as we 

 express it ; and as a consideration of the complication 

 introduced by the act of fertilization is unnecessary for 

 my argument, I will leave all question of male and female 

 germ-cells out of consideration, and treat the subject 

 as though only one cell were necessary, as is indeed often 

 the case. The germ-cell divides into two, the nucleus 

 heralding and sharing in the division. The two divide 

 to form four, the four divide into eight, the eight into 

 sixteen, and so on, until an aggregate is formed, often 



