32 BIOLOGY OF DEATH 



respect of tlie incidence of natural death is so important 

 that it requires a somewhat detailed explanation, together 

 with the reasons for it. Protozoa reproduce by a process 

 of simple division or fission. A particular individual 

 after growing to a certain size simply divides transversely 

 into two like individuials, at first smaller in size, but ra- 



FiG. 4 — Dia^am showing the process of reproduction by Fig. 5 — Conjugation 



fission in the unicellular orginism Paramecium. in Paramecium. 



pidly growing to full adult magnitude. The essential 

 gross features of this process are illustrated in Figure 4. 

 One cannot say, after the act of fission is accomplished, 

 which is parent and which is offspring. One individual 

 simply becomes two and, in the process of becoming two, 

 loses totally its own identity as an individual. Upon occa- 

 sion another process known as conjugation may intervene. 

 In this process two individuals mate together. By a 

 process of assortative mating, like sizes pair together, 



