40 THE DOCTRINE OF DESCENT. 



nation. By this we mean to say that in the province of 

 reproduction the Hmits of inquiry are neitlier narrow 

 nor pecuUar. We will therefore now proceed to describe 

 the process of reproduction and development in the 

 animal kinG:;dom. 



If, as must be generally admitted, the most essential 

 characteristics are common to the highest and the lowest 

 life, — and it is only the complexity of the vital processes, 

 together with the variety of the parts by which they are 

 performed, that give rise to graduated diversities, — it 

 will, of course, be in the simplest organisms that we shall 

 most readily recognize the nature of these vital processes. 



The simplest beings, discovered by Haeckel, such as 

 the Protamceba, those minute albuminous masses of sar- 

 code, increase to a certain extent. Why these dimensions 

 should v^ary only within definite narrow limits, and why, 

 on attaining a certain extent, the molecules should 

 gravitate into two halves, we do not know ; at any rate 

 it is an affair of relations of cohesion, theoretically 

 susceptible of computation. It is enough that at a 

 certain size the coherence of the parts is loosened in a 

 central zone, the individual becomics faithless to its 

 name, and divides into two halves, of which each from 

 the moment of separation begins an individual life, 

 while from the commencement of the fission prepara- 

 tions were being made for their self-dependence. This 

 is the simplest case of reproduction, a multiplication 

 by division. Frequently, however, it does not stop 

 at bisection ; the motion of the minute constituents, 

 which causes the fission, proceeds in such a manner that 

 the halves are again divided, and the quarters yet again, 

 the whole being thus divided into a greater number of 



