INTRODUCTORY 1 1 



perfect health. Sometimes they were purposely starved, and this 

 hastened the time when conjugation became necessary, if they 

 were to survive. But in either case whether decrepitude was 

 due to excess of fission or to unhealthy conditions conjugation 

 brought renewed vitality, unless, as it did in some cases of ex- 

 treme exhaustion, it took place between members of the same 

 stock, descendants of the same individual. 



This is a very brief account of very ingenious and long- 

 continued experiments that are fully and clearly described by 

 M. Maupas himself. 1 It is impossible not to admire the clever- 

 ness of the methods by which he keeps his specimens under 

 observation. And difficult as it must have been, even with the 

 best of methods, to count the hundreds that sprang from a single 

 isolated individual, yet he seems to have succeeded. His totals 

 are not far out, though of course not absolutely accurate. His 

 patience is no less conspicuous than his ingenuity. By repeated 

 experiments on many species he accumulates evidence that puts 

 his theory of rejuvenescence by conjugation on a firm basis. 



Thus much on the subject of the Amceba and the Infusorians. 

 Lower in the scale come the bacteria or microbes, the best known 

 form of which is shaped like a rod pinched in the middle, and 

 having a flagellum at either end. The bacteria, so far as is known, 

 multiply by an endless series of fissions ; conjugation never inter- 

 venes to break the interminable succession. In the lowest of the 

 one-celled organisms no structure or organisation has been dis- 

 covered ; no nucleus is visible. But it would be wrong to assume 

 that none exists, simply because it cannot be seen. For in the 

 cell from which a horse, for instance, is to grow there must be 

 an elaborate organisation representing the animal that is to de- 

 velop from it, but the eye, aided by the most powerful micro- 

 scope, can detect nothing of it. 



The infusorian, as we have seen, multiplies by fission for a From Pro- 

 number of generations, after which senility sets in, and with Meuz 

 conjugation comes a rejuvenescence. Now if, when a cell 



1 See M. Maupas' two papers in the Archives de Zoologie experimental et generate : La 

 multiplication des infusoires cities, 1888, and Le Rajcunissement Karyogamique chez les cities, 

 1889. 



