PHENOMENA ACCOMPANYING FERTILIZATION 295 



first meiotic or maturation division; Phase C, the period of the 

 second meiotic division ; Phase D, the third nuclear division result- 

 ing in the formation of the pronuclei; Phase E, the period of in- 

 terchange and union of pronuclei; Phase F, the period of the first 

 metagamic nuclear division; Phase G, of the second metagamic 

 division, and Phase H, the period between the second metagamic 

 nuclear division and the first division of the reorganized cell. 



The first four of these phases have to do with the phenomena of 

 maturation, the last four with the process of reorganization of 

 the individual. In Trachelocerca phoenicopterus this succession of 

 stages according to Lebedew (1908) is entirely absent and fertili- 

 zation follows quite a different course. Also in Euplotes charon 

 and Euplotes patella according to Maupas there is a slight varia- 

 tion in the usual sequence in that an anomalous, additional or 

 preliminary division of the micronucleus takes place in each con- 

 jugant prior to the first of the two maturation divisions. In the 

 Peritrichida also a similar preliminary division occurs but in these 

 cases it is limited to the microgamete, the macrogamete following 

 the usual history (Vorticella monilata, I . nebulifera Maupas; 

 Carchesium polypinum Maupas, and Popoff, 190S; Ophrydium 

 versatile Kaltenbach, 1915; and Opercularia coarctata Enriques, 

 1907). In the Ophryoscolecidae according to Dogiel (1925) similar 

 progamous nuclear divisions are followed by division of the cells 

 resulting in much smaller conjugating individuals. 



If more than one micronucleus is normally present in the ciliate 

 the first meiotic division usually takes place in all of them and the 

 second division may occur in all, or one or more of the products 

 of the first division may be absorbed in the cell. Some multiple 

 micronuclei have been described in conjugating forms of Paramecium 

 aurelia (Hertwig, 1889), Onychodromus grandis (Maupas, 1889), 

 Stylonychia pustulata (Maupas, 1889; Prowazek, 1899) and Oxytricha 

 fallax (Gregory, 1923) each individual having 2 micronuclei. Two 

 or 3 micronuclei are present in conjugating Didinium nasutum 

 (Prandtl, 1906); 2 to 4 in Uroleptus mobilis (Calkins, 1919); 4 or 5 

 in Blepharisma unduians (Calkins, 1912) and 16 to 18 in Bursaria 

 truncatella (Prowazek, 1899). 



1. Phase .1. The Prophase Stages of the First Meiotic Division.— 

 In many ciliates in which the history of maturation has been followed 

 there is very little to distinguish the first meiotic mitosis from the 

 usual vegetative divisions beyond a slight swelling of the micronu- 

 cleus, fragmentation of its homogeneous chromatin and formation 

 of its chromosomes. This appears to be the case in Loxophyllum 

 meleagris (Maupas, 1889), Spirostomum teres (Maupas, 1889), 

 Euplotes patella (Maupas, 1889), Colpidium colpoda (Hover, 1899), 

 and in Blepharisma unduians (Calkins, 1912). In the case of 

 Colpidium colpoda Iloycr (1899) described a typical tissue-cell 



