322 BIOLOGY OF THE PROTOZOA 



fixed and stained to determine the stage of maturation. The other 

 arm is cultivated. Since other pronuclei usually degenerate, it is 

 evident that only one pronucleus is present in the piece cultivated, 

 and this one contains the haploid number of chromosomes. The 

 possibility remains open, however, that this pronucleus may unite 

 with a sister pronucleus formed by sister nuclei, and which do not 

 degenerate, but for this there is no evidence. In this case it would 

 be parthenogenesis of the third type above. When such cutting 

 experiments are successful the resultant organisms regenerate per- 

 fectly and undergo typical life histories and each individual has the 

 normal number of chromosomes. 



The most probable interpretation of such merotomy experiments 

 appears to be that the diploid number of chromosomes is restored 

 by chromosome division. 



The conclusion follows that so far as chromosomes are concerned, 

 endomixis and amphimixis after prolonged in-breeding as in Urolep- 

 tus are similar in results. The cellular processes of reorganization 

 are identical in both and Woodruff is quite right in stating that 

 amphimixis is unnecessary for continued life of a ciliate. In respect 

 to vitality, endomixis and amphimixis are equivalent and so long as 

 one or the other occurs continued vitality is possible. Furthermore 

 it may be argued that if an equivalent reorganization is accomplished 

 in any other way then neither endomixis nor amphimixis by conjuga- 

 tion is necessary. Evidence of this third possibility is furnished by 

 observations on Actinophrys .sol (Belaf, 1922) and by the animal 

 flagellates. If this is a correct interpretation then there is a possi- 

 bility of harmonizing the many conflicting results and views 

 advanced in relation to the much discussed problem of indefinitely 

 continued vitality. 



B. Autogamy.— Autogamy or self-fertilization in Protozoa is a 

 logical sequence of endogamy. If a gamont of Actinophrys sol 

 should not divide to form gametes which later fuse (see above, p. 

 308), and if the gamont's nucleus should divide and the two products 

 should undergo meiosis, and the two pronuclei should then unite, 

 all in the same one cell, then the process would be called autogamy. 

 Or if pronuclei from the same individual ciliate should unite, it 

 would be autogamy. In short autogamy is the realization of 

 Type 3 of parthenogenesis above. 



The phenomena which have been described and interpreted as 

 autogamy, particularly as they occur in parasitic forms, are rather 

 cautiously interpreted today and many careful observers, perhaps 

 too careful, are inclined to regard the earlier descriptions of autog- 

 amy as dealing with degeneration phenomena rather than with 

 normal vital activities. One illustration, that of Sappinia diploidea, 

 appears to be well established. The organism has two nuclei which 

 lie closely together (Fig. 163). Both nuclei divide at cell division 



