Physiology and Biology of the Protozoa. 489 



the daughter-individuals are of course increased in the follow- 

 ing- generations, so that in the case of the granddaughters 

 and great-granddaughters of a common ancestral individual 

 we can no longer speak of simultaneous division ; in these 

 differences of manj hours and even of days occur. As the 

 same share of nuclear substance fails to the two congruent 

 halves into which the Infusorian breaks up in division, and 

 indeed, as we assume, to each of them one of the mor- 

 phologically and physiologically equivalent halves of the 

 original nucleus, it might be supposed that under the same 

 external conditions therefore (for example, those of com- 

 mon residence in a very small quantity of water) the daughter- 

 nuclei must be absolutely alike in the exertion of their dominion 

 over the plasma, and therefore in their influence upon division, 

 so that in the daughter-individuals increase will take place 

 at the same moment. Why small ditFerences should occur I 

 cannot at present say definitely; 1 believe, however, that in this 

 circumstance we may see an indication that the morphological 

 and 'physiological congruency of the two daughter-individuals 

 ■produced hy divisio7i is by no means quite an absolute one. 



1 may remark further that in other Infusoria, such as 

 Clymacostoiniim, Stylonychia, and Paranuecium^ I have also 

 been able to prove the (nearly) simultaneous multiplication 

 of the daughters of the same individual. 



As regards the time that intervenes between the different 

 divisions, I can only say anything definite in relation to 

 Ste?itorj as this, hitherto, is the only Infusorian in which I 

 have succeeded in making a number of observations upon thj^ 

 point. Singularly enough it appeared that division took place 

 in most cases at intervals of two days^ that daughter-individuals 

 divide into granddaughters on the second day after their 

 separation, and granddaughters in another two days into great- 

 granddaughters, and so forth. In forty-two out of ffty-six 

 cases division took place always on the second day after the 

 preceding one ; six divided as early as the next day, five only 

 on the third, and three after four, five, or more days. In Stentor 

 cceruleus therefore we may almost regard it as the rule that 

 the above-raentiou'ed interval of time is maintained between 

 each two divisions. The question now, however, is whether 

 this phenomenon is normal, or whether it is called forth by 

 unnatural conditions of existence. This is difficult to decide, 

 as these investigations can only be made on isolated animals, 

 and therefore on animals living in small quantities of water. 

 But even if we suppose that the small quantity of water has 

 produced the tendency to rapid division, this would only lead to 

 the assumption that this tendency may also occur in nature 

 Ann. li; Mag. N. Hist. Ser. 5. Vol. xvii. 34 



