PHENOMENA ACCOMPANYING FERTILIZATION 545 



The most probable interpretation appears to be that the diploid 

 number of chromosomes is restored by chromosome division. In 

 endomictic animals chromosomes become homozygous. But after 

 50 or more generations of close in-breeding by conjugation the 

 chromosomes must all have become similarly homozygous and a 

 matter of no qualitative dift'erence whether one set divides, or receives 

 an homologous set in amphimixis. The 4 chromosomes of Uroleptus 

 are probably qualitatively different and a full set are probably needed 

 for complete development of the individual. There is always a pos- 

 sibility of imperfect segregation, resulting in failure to reorganize 

 on the part of the ex-con jugant. This possibility is certainly not 

 lessened by complete homozygosity and may be significant in con- 

 nection with the increased percentage of deaths after conjugation 

 which is now apparent in the cultures. 



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 Parcnnecium calkinsi (Spencer, 1925), by Actino- 

 phrys sol (Belaf, 1922), by Endorina elegans (Hartmann, 1921) 

 and by the animal flagellates. If this is a correct interpretation 

 then there is a possibility 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. 

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

 sh(juld 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 interj^reted today and many careful observers, perhaps 

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

 gamy as dealing with degeneration phenomena rather than wdth 

 normal vital activities. A classical example of such earlier work is 

 the description of autogamy in Endaniceba coli as given by Schaudinn 

 35 



