PHENOMENA ACCOMPANYING FERTILIZATION 519 



first metagamic nuclear division; Phase G, of the second meta- 

 gamic 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 yhcenicopteriis this succession of 

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

 tion follows quite a different course (page 375). Also in Euplotes 

 charon and Euplotes patella according to jMaupas there is a slight 

 variation in the usual seciuence in that an anomalous, additional 

 or preliminary division of the micronucleus takes place in each 

 conjugant 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, V. iiebulifera Maupas; 

 Carchesiiim polypinvm Maupas, and Popoff, 1908; Orphrydium 

 versatile Kaltenbach, 1915; and Opercvlaria coarctata Enriques 

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

 progamous nuclear di\isi()ns 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 Paramecmm 

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

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

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

 or 3 micronuclei are present in conjugating Didiniuni nasntum 

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

 in Blepharisma umhdans (Calkins, 1912) and 16 to 18 in Ihirsaria 

 trvncatella (Prowazek, 1899). 



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

 In many ciliates in which the histor\' 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), Spirostoimim teres (Maupas, 1889), 

 Evplotes patella (Maupas, 1889), Colpidium colpcda (Hoyer, 1899), 

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

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

 spireme but this is so exceptional among ciliates that it cannot be 

 accepted without confirmation. 



In the majority of ciliates this first meiotic mitosis is markedly 



