MODES OF REPRODUCTION. 49 



befall the "body" which bears it. In short, the asexual 

 method of liberating buds has been replaced in most animals 

 by the liberation of special germ-cells, by the more econom- 

 ical and advantageous process of sexual reproduction. 



Summary of Modes of Reproduction, 



A. In single-celled Animals (Protozoa). 



(i) The almost mechanical rupture of an amoeboid cell, 

 which has become too large for physiological equi- 

 librium (e.g., Schizogenes). 



(2) The discharge of numerous superficial buds at once 



{e.g., Arcella and Pelomyxd). 



(3) The formation of one bud at a time (very common). 



(4) The ordinary division into two daughter cells at the 



limit of growth. 



(5) Successive divisions within limited time and within 



limited space (a cyst). This results in what is called 

 spore formation, " free-cell formation," " endogenous 

 multiplication " {e.g., in Gregarines). 



B. In many-celled Animals (Metazoa). 



(Asexual.) 



{a) The separation of a clump of body-cells, e.g., from the 

 surface of some Sponges (A crude form of budding.) 



{b) The formation of definite buds which may or may not 

 be liberated ; and other forms of asexual multiplica- 

 tion. 



{Sexual.) 



{a) The liberation of cells from a simple Metazoon in 

 which there is so little division of labour that the 

 distinction between body cells and reproductive cells 

 is not marked. (Hypothetical.) 



{&) The liberation of special reproductive or germ cells, 

 which have not taken part in the formation of the 

 body, and which retain unaltered the inherent quali- 

 ties of the original germ-cell from which the parent 

 arose. (The ordinary process.) 



D 



