FERTILISATION 223 



on the other hand, a varied environment seemed to obviate the 

 necessity for conjugation in Pammoxiuin. 



He was able by continually altering the character of their food, 

 and imitating the conditions of pond life, to continue the life of a 

 single race of Pammcecium for over five years, and carry it through 

 3000 generations by simple fission without conjugation taking place. 1 

 Many of these cultures showed periods of depression followed 

 by periods of increased fission, and further investigation showed that 

 each period of depression and restoration was accompanied by a 

 special process of nuclear reorganisation which apparently replaced 

 the act of conjugation. The macronucleus breaks up and disappears, 

 the micronuclei dividing twice, but do not complete the third division, 

 which in conjugation gives rise to the gametic nuclei. A new 

 macronucleus is formed from the micronuclei, and the normal nuclear 

 organisation re-established in this way. To this process of nuclear 

 reorganisation Woodruff has applied the name of "endomixis." The 

 question of endomixis has been studied by Erdmann, 2 who comes to 

 the conclusion that new lines of Paranuecium originate after this 

 process, and are made constant by selection ; that is, heritable 

 variations occur in asexually conducted lines, and that the rigid 

 conception of the ganotype does not hold true for Protozoa. If a 

 pure line of Paramcecium is transferred to new environmental 

 surroundings, it answers immediately to this change by the pro- 

 duction of endomixis. The necessary opportunity is then given 

 for the survival of those individuals of the new stock in equili- 

 brium with their new surroundings. This process is constantly 

 taking place in nature, for if a roadside pool partially dries 

 up, or a heavy fall of rain takes place, its chemical character 

 may lie altered, but the Paramwcia inhabiting the pool are 

 enabled to adjust themselves to the change through the process 

 of endomixis. 3 



It may seem a far cry from the Ciliate Infusorian to the British 

 thoroughbred horse, yet there is evidence that here also an in-bred 

 and relatively infertile race may be rejuvenated through access to new 

 surroundings. Allison, referring to blood stock of British origin, 

 born in Australia and New Zealand, writes as follows : " We can 

 draw from these, not only strains of blood which we have lost, but 

 horses and mares, born again, so to speak, and admirably suited to 



1 Woodruff, "Rhythms and Endomixis in Various Races of 

 aurclia" Biol. Bull., vol. xxxiii., 1917 ; see also Woodruff and Erdmann, 

 "Abnormal Periodic Reorganisation Process without Cell-Fusion in Purn- 

 mcerium," Jour, of Exp. Zool., vol. xvii., 1914 ; and Jennings, !(. cit. 



- Erdmann, " Endomixis and Size Variations in Pure Bred Lines of 

 Paramascium aurelin" A /</>. f. AW //</. d. Orrimn'sm, vol. xlvi., 1920. 



3 Mr. Saunders informs me that in England roadside pools frequently 

 undergo great changes of H'-ion concentration after rain storms. 



