122 LIFE AND DEATH. 



becomes a form of reproduction when it is associated with the 

 division of the encysted animal. Simple division was the true 

 and original form of reproduction in Monoplastides, and even now 

 it is the principal and fundamental form. 



Hence we see that among 1 the Monoplastides reproduction is not 

 connected with death, even if we accept Gotte's view and allow 

 that encystment represents death. I shall return later on to the 

 relation between death and reproduction in the Metazoa ; but the 

 question first arises whether encystment, if it is not death, has any 

 analogue in the higher animals, and further whether death takes 

 that place in their development which is occupied by encystment in 

 the Monoplastides. 



Among the higher Metazoa there can be no doubt as to what 

 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 im- 

 mortal 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 

 (soma) 1 . 



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 re- 

 production ? 



Gotte believes that the natural death of these organisms (which 

 he rightly calls Homoplastides) consists in ' the dissolution 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, 



1 I trust that it will not be objected that the germ-cells cannot be immortal, be- 

 cause they frequently perish in large numbers, as a result of the natural death of the 

 individual. There are certain definite conditions under which alone a germ-cell can 

 render its potential immortality 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 ensured for the species. 

 If in the natural death of the individual the germ-cells must also die, the natvra 

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



