2 3 8 



THE EVOLUTION OF SEX. 



exhaustion. The males of some spiders normally die after fertilizing 

 the female, a fact perhaps helping to throw light upon the sacrifice of 

 others to their mates. The similarly tiny (ultra-katabolic) male 

 rotifer— an ideal but too unpractical lover, with not even an alimentary 

 canal — would seem usually to fail and expire prematurely, leaving the 

 female to undisturbed parthenogenesis. Every one is familiar with the 

 close association of love and death in the common mayflies. 

 Emergence into winged liberty, the love-dance and the process of 

 fertilization, the deposition of eggs and the death of both parents, are 

 often the crowded events of a few hours. In higher animals, the 

 fatality of the reproductive sacrifice has been greatly lessened, yet 

 death may tragically persist, even in human life, as the direct nemesis 

 of love. 



The temporarily exhausting effect of even moderate sexual 

 indulgence is well known, as well as the increased liability to all forms 

 of disease while the individual energies are thus lowered. 



XI. Organic Immortality. — Comparatively little is yet known 

 about the length of life among lower animals, but there is no reason to 

 doubt that all multicellular organisms die. We have just emphasized 

 the view of Goette and other naturalists, that reproduction is the 

 beginning of death; which is not inconsistent with the apparent para- 

 dox that local death was the beginning of reproduction. Allowing, 

 then, that multicellular organisms at any rate are mortal, and that the 

 verv blossoming of the life in reproduction is fated with a prophecy of 

 death which r is its own fulfillment, we have to face two questions, — 

 What of death in the Protozoa? and, In what sense is there an immor- 

 tality throughout the organic series ? 



Often enough already, in the preceding pages, we have had to 

 reiterate the contrasts between the Protozoa and the higher animals. 

 These firstlings are physiologically complete in themselves, and have 

 at least very great, if not unlimited, powers of self-recuperation. They 

 leave off where higher animal life begins, that is to say, in a unicellular 

 state. They do not form bodies. Their reproduction, moreover, is 

 in the majority simple cell-division into two. If there be loss of indi- 

 viduality, there is hardly loss of life. Death is not so serious when 

 there is nothing left to bury. Nor in most cases can one half of the 

 divided unit be the mother individual, and the other the daughter, for 

 the two appear indistinguishably the same. Thus an idea, broached 

 long ago by Ehrenberg, has been revived and elaborated by several 

 naturalists, and especially by Weismann, that the Protozoa are virtu- 

 ally immortal. 



In Weismann' s own words, " Natural death occurs only among 

 multicellular organisms, the single-celled forms escape it. There is no 



