Variations from the usual number of both macro-and micronuclei in Infusoria have been described by several investigators, Hertwig ('8&'89), Calkins ('04), Popoff ('07, '09), etc. Popoff ('09)' Sun ('12) and Kasanzeff ('01) have shown that these nuclear changes can be induced by various means (starvation, temperature and chemical treatment). Hertwig (lx.), Popoff (1.c.) and Sun (1.c.) have pointcd out the similarity between these stages and those occurring in conjugation, and the two former authors have compared them to parthenogenesis in the metazoan egg, which can here, as there, be artificially induced (Popoff, '09). This interpretation has been amplified by Woodruff and Erdmann ('14, '16) and accepted by Calkins ('15)' although the former writers have proposed the term 'endomixis' instead of 'parthenogenesis' for this phenomenon.
According to these latter writers nuclear re-organization serves to rejuvenate a depressed race. This interpretation seemingly contradicts the work of Jennings ('13), who has shown that conjugation does not result in rejuvenation, but is to be interpreted as a means of producing bi-parental inheritance and variability in the 0ffspring.l Woodruff and Erdmann (1.c.) have shown further that the occurrence of endomixis does not necessarily accompany a depression period (see line 111, p. 480). Regarding this irregularity the authors state that it "is an exception for which the data afford no adequate explanation." Their graphs (text figs.