150 On the Genetics of the Giliate Protozoa 



individual possessing at its formation a normal karyoplasmic ratio. And 

 so the cycle of events continues. 



48. Pojjoff' (1909) obtained confirmatory results with I'arainecium. 



P 



The value of .-> and the rate of division vary with the temperature in 



both cases; but the general conclusions given above appear valid for all 

 experiments, mutatis mutandis. 



49. The " moment of karyoplasmic tension " is the moment at 

 which division is determined. If this were not so, indeed, it would 

 be difficult to understand how any division could occur'. Popotf ( 1 908) 

 established this by ingenious vivisection experiments. The karyo- 

 plasmic ratio of a Frontonia was changed by cutting ofif a piece of its 

 cytoplasm. If this was done during the period oi'fitiietiunal growth, the 

 cytoplasm continued to grow until the normal karyoplasmic ratio was again 

 established. Division was consequently delayt^d, but finally took place 

 in the usual way. If, however, a piece of cytoplasm was removed during 

 the period of division growth, the animal did not regulate its karyo- 

 plasmic ratio by compensatory growth of cytoplasm ; but it divided at 

 the proper time (I7th hour) with an abnormal karyoplasmic ratio. This 

 seems to indicate that the moment of karyoplasmic tension determines 

 division. And, moreover, Popoff elicited the curious fact that the plane 

 of division is also determined at this moment : for an animal from which 

 cytoplasm had been removed during the period of division growth 

 divided, into two unequal-sized individuals, at the plane which would 

 have been median had the animal been whole. 



50. Moody (1912) has made .some measurements of Spathidium 

 which — she believes — tally with Popoff's results for Frontonia and 

 Paramecium (§§ 47, 48). But unfortunately no real confirmation of 

 his laborious and important researches has yet appeared. It is easy 

 to criticize or disbelieve his conclusions, but to test them by further 

 experiments performed in the same manner is an arduous task. And 

 without further experimental evidence, criticism of this work becomes 

 merely an academic discussion of probabilities — of no real value. 



51. Inquiries have been instituted into the effects of chemical and 

 physical agents upon the rate of fission in ciliates, and some results of 

 this work may suitably be considered here. We have already seen 



' In the case cited above, for example, it will be seen that the karyoplasmic ratio is 

 normal (67) just before division. As it is the same in the uewly divided organism, one 

 naturally asks why division should occur at all — assuming it to be determined by the 

 karyoplasmic ratio. Some such explanation as that given above therefore becomes 

 necessary. 



