GENEOLOGICAL. 395 



unicellular organisms and not with embryos, this 

 seems the fittest place to take note of both, and it 

 must be remembered that the Protozoa and Proto- 

 phyta stand to the whole race of animals and plants 

 in somewhat the same relation as the germ-cells and 

 embryos do to individual organisms. 



As the result of a long series of observations 

 models of patient accuracy Maupas reached the 

 general conclusion that sexual union in ciliated In- 

 fusorians, dangerous perhaps for the individual life, 

 a loss of time so far as immediate multiplication is 

 concerned, is necessary for the continued vigour 

 of the race. The life runs in cycles of asexual 

 division, which are strictly limited. Conjugation 

 with unrelated forms must occur, else the whole 

 life ebbs. Without it, the Protozoa, which some 

 have called " immortal," die a natural death. Con- 

 jugation is the necessary condition of their eternal 

 youth and immortality. Even at this low level, 

 only through the fire of love can the phoenix of the 

 species renew its youth.* 



(1} Regeneration Experiments. In the eight- 

 eenth century, the attention of naturalists was for 

 a time focussed on the problem of the regeneration or 

 regrowth of lost parts. Trembley discovered to his 

 great delight that the fresh-water polyp (Hydra) 

 might be multiplied by being cut in pieces; Spal- 

 lanzani showed that the earthworm cut by the spade 

 might regrow a new tail or even a new head; Bon- 

 net made numerous experiments on other worms, 

 and thought out an elaborate theory; Reaumur 

 pointed out the advantage of the regenerative capac- 

 ity in animals which were in their natural condi- 

 tions exposed to frequent risks of breakage or 

 *See Evolution of Sex (4th ed., 1901), pp. 176-78, 



