172 Tlie Study of Animal Life part m 



multiply. But in the single -celled Protozoon all the pro- 

 cesses of life occur within a unit mass of living matter. In 

 the many-celled Metazoon the various processes occur at 

 different parts of the body, are discharged by special sets of 

 cells, among which the labour of life has been divided. The 

 life of the Protozoon is like that of a one -roomed house 

 which is at once kitchen and work-room, nursery and coal- 

 cellar. The life of the Metazoon is like that of a mansion 

 where there are special rooms for diverse purposes. 



In having no " body " the Protozoa are to some extent 

 relieved from the necessity of death. Within the compass 

 of a single cell they perform a crowd of functions, but tear 

 and wear are often made good again, the units have great 

 power of self- recuperation. They may, indeed, be crushed 

 to powder, and they lead no charmed life safe from the 

 appetite of higher forms. But these are violent deaths. 

 What Weismann and others have insisted on is that 

 the unicellular Protozoa, in natural conditions, need never 

 die a natural death, being in that sense immortal. It 

 is true that a Protozoon may multiply by dividing into two 

 or more parts, but only a sort of metaphysical individuality 

 is thus lost, and there is nothing left to bury. We would 

 not, however, give much prominence to a strange idea of 

 this kind. For the " immortality of the Protozoa " is little 

 more than a verbal quibble ; it amounts to saying that our 

 common idea of death, as a change which makes a living 

 body a corpse, is hardly applicable to the unit organisms. 

 I believe, moreover, that the idea has been exaggerated ; 

 for instance, the Protozoa in the open sea, in their natural 

 conditions, seem to die in large numbers. 



The combination of all the vital activities within the 

 compass of a single-cell involves a very complex life within 

 the unit, — not more complex than the entire life of a many- 

 celled animal, but fuller than that of one of its component 

 cells. Wliile a Protozoon is relatively simple in structure, 

 its life of crowded functions, such as moving, digesting, 

 breathing, is exceedingly complex. The simpler an organism 

 is in structure the more difficult will it be to study its separate 

 functions. Physiological or functional simplicity is in inverse 



