298 DARWINISM AND THE PROBLEMS OF LIFE 



globule about the size of a pin's head, consisting of a 

 number of cells. It is often found in large quantities 

 in our ponds. In this animal we have the first division 

 of labour. Most of the cells have taken charge of the 

 functions of movement and nutrition ; a few others of 

 a different shape are responsible for reproduction. 

 These lie in the centre of the other cells, and can 

 by repeated cleavage create a new animal, which 

 detaches itself from the mother and swims about. If 

 the parent has given up all its germ-cells, it dies off, 

 since its other cells cannot produce germ-cells. 



There does not seem to be anything more wonderful 

 in the reproduction of the protozoa. Two quite equal 

 halves are formed by cleavage, and each of them has 

 only to grow, not to form anything new. It is the same 

 with the pandorina, only in this case the cleavage is 

 repeated three times, and produces sixteen cells which 

 remain united. It is in the volvox that the marvel of 

 heredity first appears. Here the germ- cell reproduces 

 not only its kind, but also the very different cells of the 

 body. But there is no sudden leap from the protozoa 

 to the volvox. There are many protozoa in which the 

 fore end differs a good deal from the hind end ; and 

 when such an animal divides, each half must reproduce 

 features that it does not possess. Mere growth could 

 not convert fragments of these animals with different 

 parts into whole individuals. 



We can more or less understand the mystery of 

 heredity with the aid of the above theory. Even the 

 protozoon contains rudimentary parts in its nucleus, 

 which can build up the different parts of the cell 



