The Message of Science. 67 



agtfleba has eve r lost an ancestor by death." Weismann de- 

 fines death as " a definite arrest of ^e. The proof of 

 death is that the organized substance which previously 

 ^aye_rise to the phenomena of life foj ;eveiLceases-tO-0£iffir 

 nate such phenomena." Death implies the presence of 

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

 spring by dividing into two amcebse. 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— pFetozooiis__ 

 die only from iaei^enta_af_ heat, coldi_ox_Yiolencfi. 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 wliich 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 reproductiv.e.cells) are the units from which the 

 next generation will be developed. The somatic cells are 



