REPRODUCTION ii 



sexual mating. This will at once become apparent from 

 the fact that there are numerous classes of low organisms 

 which are sexless, and in which reproduction can accord- 

 ingly only be asexual. The only element discernible in the 

 process of reproduction is here clearly nothing else than 

 the propagation of the species. 



A. Asexual Reproduction. 



If we now turn to the cases of asexual reproduction, we 

 find them chiefly among the lower classes of organisms. It 

 is the ordinary method of propagation among the one-celled 

 plants and animals. But it is by no means restricted to 

 them, as we find asexual reproduction as high up in the 

 animal kingdom as the worms and tunicates (sea-squirts), 

 and as a regular occurrence in the branching of flowering 

 plants. 



We can distinguish three kinds of asexual reproduction : 

 (a) Division ; (b) Budding ; and (c) Sporulation. 



{a) Division. 



The simplest process of Division we find in the one- 

 celled organisms. Here — as, e.g., in the Amoeba or In- 

 fusorian — we have a single cell, which, after attaining a 

 certain size, divides into two daughter-cells. This process 

 starts with the nucleus, which elongates, becomes dumb- 

 bell-shaped, and finally breaks up into two halves. The 

 contents of the cell-body follow suit, become indented, and, 

 by surrounding the two newly-formed nuclei, bring about 

 the formation of two separate individual daughter-cells. 

 This process of division, which is called " Amitosis," shows 

 clearly that reproduction as just described is nothing but 

 the outcome of growth. The single mother-cell, becoming 

 too large for carrying on the process of nutrition, simply 

 splits up into two constituent halves, which, as it were, are 

 a continuation of its own existence. 



