III.] LIFE AND DEATH. 1 23 



we mean by death, but the precise nature of that which dies is 

 not equally evident, and the popular conception is not sufficient 

 for us. It is necessary to distinguish between the mortal and 

 the immortal part of the individual— the body in its narrower 

 sense {soma) and the germ-cells. Death only affects the former ; 

 the germ-cells are potentially immortal, in so far as they are 

 able, under favourable circumstances, to develope into a new 

 individual, or, in other words, to surround themselves with a 

 new body {somay. 



But how is it with the lowest Polyplastides in which there is 

 no antithesis between the somatic and germ-cells, and among 

 which each of the component cells of the multicellular body 

 has retained all the animal functions of the Monoplastides, even 

 including reproduction ? 



Gotte believes that the natural death of these organisms 

 (which he rightly calls Homoplastides) consists in 'the disso- 

 lution of the cell-colony.' As an example of such dissolution 

 Gotte takes Hackel's Magosphaera planula, a marine free- 

 swimming organism in the form of a sphere composed of a 

 single layer of ciliated cells, imbedded in a jelly. (For figure 

 see p. 124.) This organism cannot however be ' considered as 

 a genuine perfect Polyplastid, for at a certain time the com- 

 ponent cells part from one another and then continue to live 

 independently in the condition of Monoplastides.' These free 

 amoebiform organisms increase considerably in size, encyst, 

 and finally undergo numerous divisions — a kind of segmen- 

 tation within the cyst. The result of the division is a sphere 

 of ciliated cells similar to that with which the cycle began. 

 In fact, Magosphaera is not a perfect Polyplastid, but a transi- 

 tional form between Polyplastides and Monoplastides, as the 

 discoverer of the group of animals of which it is the onl}' 



^ I trust that it will not be objected that the germ-cells cannot be 

 immortal, because they frequently perish in large numbers, as a result ot 

 the natural death of the individual. There are certain definite con- 

 ditions under which alone a germ-cell can render its potential im- 

 mortality actual, and these conditions are for the most part fulfilled 

 with difficulty (fertilization, etc.). It follows from this fact that the 

 germ-cells must always be produced in numbers which reach some 

 very high multiple of the necessary number of offspring, if these latter 

 are to be insured for the species. If in the natural death of the 

 individual the germ-cells must also die, the natural death of the soma 

 becomes a cause of accidental death to the germ-cells. 



