Chap, xni.] REPRODUCTION OF PROTOZOA. 473 



the performance of that part of his life-work which 

 affects his race, the individual reproduces his kind. 



This process of reproduction may be one of two 

 modes, it may either be sexual or asexual ; that is 

 to say, two different cell elements may unite to form 

 a single cell from which others arise, or one kind of 

 cell element alone may form a new individual. 



The latter is obviously a more simple method than 

 the former, and it is the only one which is certainly 

 known to obtain in the Protozoa. Here, too, as 

 our previous studies would lead us to expect, there is 

 no distinct differentiation of any special organ ;* we 

 have the phenomenon, but not the organ. 



As has been already pointed out in the case of the 

 Amoeba (see page 22), the simplest method of repro- 

 duction is that in which the mass of protoplasm under 

 observation divides into halves of about the same size. 

 Each of these halves is, save in size, a copy of the 

 parent; which, ipso facto, has disappeared. This 

 method of reproduction is known as Fission, and it 

 is exceedingly common among the lower organisms. 

 In some cases a process of non-nucleated protoplasm 

 separates from the body of the Amoeba ; and this bud- 

 like outgrowth, increasing in size and acquiring a 

 nucleus, shortly comes to have the form and structure 

 of its parent. This is the process by Oemmation. 



Yet a third mode of reproduction, which may be 

 called, that of endo-spore formation, has been ob- 

 served in some of the Protozoa ; but it, like the 

 methods of fission and gemmation, does not require 

 the influence of another individual ; like them, it is 

 absolutely asexual. The protozoon, becoming qui- 

 escent, forms around itself an envelope or cyst, which 

 is at first transparent, and which completely encloses 



* The action and influence of the nucleus of a cell is so obscure 

 that the part which it possibly takes in initiating cell-division 

 cannot be discussed in an elementary work. 



