The Message of Science. 67 



amoeba has ever lost an ancestor by death." Weismann de- 

 fines death as "a definite arrest of life. The proof of 

 death is that the organized substance which previously 

 gave rise to the phenomena of life forever ceases to origi- 

 nate such phenomena." Death implies the presence of 

 something dead. An amoeba, for example, produces off- 

 spring by dividing into two amoebae. By this act of 

 fission the parent disappears in the two children, but has 

 not died. Hence arises Weismann's conception of the 

 natural immortality of the protozoons. The protozoons 

 die only from accidents of heat, cold, or violence. This 

 view, however, has now of necessity to be modified. 



(2) These deductions apply not only to protozoons, but 

 essentially to all living creatures which produce offspring 

 by fission ; and it is on this basis that Weismann has built 

 up his theory of the origin of death, briefly this : Since 

 amoebae and other unicells which reproduce by fission are 

 naturally immortal, death must be regarded as peculiar to 

 multicellular organisms (metazoa). In the metazoa where 

 the cells are organized with differentiation of function, 

 there are two distinct classes or groups, those which 

 develop to form the animal body (soma), and the repro- 

 ductive cells, confined to the generative tract. The 

 former (somatic cells) grow till the organic limits are 

 reached, live for a time and fall into senescence ; the lat- 

 ter (the reproductive cells) are the units from which the 

 next generation will be developed. The somatic cells are 



