166 On the Genetics of the Ciliate Protozoa 



94. Hunger was believed by Maupas (§ 20) to induce conjugation 

 in cultures containing sexually mature individuals. The ert'ects of 

 hunger upon the organism have since been specially studied by 

 Wallengren (1901 a, — Paramecium and Colpidium) and Kasanzeff 

 (1901, — Paramecium). Wallengren finds that hunger produces de- 

 generative changes in the cytoplasm (vacuolation, etc.) and meganucleus 

 (fragmentation, etc.), but not in the micronucleus. Starved individuals 

 are of conspicuously smaller size. These observations are confirmed by 

 Calkins (1904). Kasanzeff finds that starvation leads to an increase in 

 the size of the meganucleus. And R. Hertwig (1899, 1902, 1905, etc.) 

 has been led by these and similar observations to formulate the following 

 raisoii d'etre of conjugation — based upon his hypothesis of the karyo- 

 plasmic ratio (§ 30) : In the course of normal functional activity of the 

 organism, or as a result of hunger, the meganucleus grows at the 

 expense of the cytoplasm, thus causing an increasing disproportion 

 in the mass-relations of the one to the other. This disproportion may 

 be compensated by a reorganization of the nuclear apparatus : and 

 conjugation therefore takes place in order to bring about this result. 

 Conjugation is thus regarded as a means of regulating the karyoplasmic 

 ratio. Some remarkable experiments inspired by this idea have since 

 been made. 



95. It will be recalled that the meganucleus is relatively larger 

 in ciliates kept at a low temperature than in those kept at a high 

 temperature (§ 66). It therefore occurred to Prandtl (1906) that if 

 he were to subject organisms adapted to a low temperature suddenly 

 to a higher, they would find themselves in an abnormal condition in 

 which the meganucleus was too large. In other words, the condition 

 which normally leads to nuclear reorganization through conjugation 

 could be thus brought about experimentally. A sudden change of 

 this sort ought, therefore, to lead to conjugation. The experiment 

 was tried with Didinium and Dileptiis, and with successful results. 

 Conjugation took place at the higher temperature. It should be noted 

 that in these experiments temperature was not the only factor con- 

 cerned. For Prandtl supplied his animals with plentiful nourishment 

 at room temperature, and then starved them at the subsequent tem- 

 perature of 25° C. Similar experiments were made on the vorticellid 

 Carchesium' by Popoff (1908 ((), with a like successful result. He found 

 further that starvation coupled with lowered temperature favoured the 

 production of males : whereas coupled with raised temperature it led to 



' Wrongly stated to have been Epixti/lis in an earlier paper (Popoff, 1907). 



