LETHALITY OF THE METAZOA. 343 



undergoes progressive . decay, and finally they 

 perish — the decay and destruction being perhaps 

 in principle accidental, but, irl fact, they are the 

 rule. 



The different anatomical elements of the organism 

 are more or less sensitive to those perturbations which 

 cause senescence, necrobiosis, and death. There are 

 some more fragile and more exposed. Some are 

 more resisting, and finally, there are some which 

 are really immortal. We have just said that the 

 sexual cell, the ovum, is one. It follows that the 

 metazoan, man for instance, cannot entirely die. 

 Let us consider one of these beings. Its ancestors, 

 so to speak,^ have not entirely disappeared ; each has 

 left the fertile egg, the surviving element from which 

 has issued the being of which we speak ; and when 

 it in its turn has developed, part of that ovum has 

 been placed in reserve for a new generation. The 

 death of the elements is not therefore universal. 

 The metazoan is divided from the beginning into 

 two parts. On the one hand are the cells destined 

 to form the body, somatic cells. They will die. On 

 the other hand are the reproductive, or germinal, or 

 sexual cells, capable of living indefinitely. 



Somatic and Sexual Cells. — In this sense we may 

 say with Weismann that there are two things in 

 the animal and in man — the one mortal, the soma 

 the body, the other immortal, the germen. These 

 germinal cells, as in the case of the protozoa we 

 mentioned above, possess a conditional immortality. 

 They are imperishable, but on the contrary, are 

 fragile and vulnerable. Millions of ova are destroyed 

 and are disappearing every moment. They may die 

 by accident, but never of old age. 



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