236 SEX IN MICROORGANISMS 



though size of conjugants did depend on previous history, mostly 

 relating to nutritional conditions. Thus, in many ciliates conjugants 

 are smaller than non-conjugants but may be essentially of the same 

 size, and Pearl (1907), Jennings (1911), and others have claimed 

 that selective mating takes place, since, on the average, members of 

 pairs of conjugants are more alike in size than non-conjugants chosen 

 at random. 



Pregametic Nuclear Phenomena 



The number of pregametic mitoses in the Euciliata is relatively 

 constant. There are certain other features that are generally found. 

 The preparation for the first division (second in Euplotes) is a period 

 of long duration, usually with special configurations of the intra- 

 nuclear material. Species of Farameciwn commonly show a "crescent" 

 or "sickle" stage (Fig. AA, 3, at right) while many other ciliates 

 show a "parachute" or "candelabra" stage (Fig. AJ, 13; AL, 1). 

 Wichterman (1940) estimated that the time from first association of 

 conjugants to the first metaphase lasted lYi hours in Farameciwn 

 caudatwn, the total time of attachment being about 13 hours. Since 

 this first division is the first of the two meiotic or maturation divisions, 

 and the micronucleus increases greatly in size, it is generally assumed 

 that this size increase corresponds to the growth stage in metazoan 

 gametogenesis. Most authors report "reduction" in the second of 

 these divisions. In harmony with metazoan conditions, one would 

 expect this first division to involve synapsis of homologous chromo- 

 somes and the formation and division of a haploid number of tetrads 

 which would separate into dyads on the mitotic spindle. However, 

 ciliate chromosomes frequently do not show the pattern of behavior 

 that one finds in the typical metazoan first gametocyte nucleus. In 

 Euplotes patella (Turner, 1930) there are four pregametic nuclear 

 divisions after the conjugants have become joined. The first division 

 follows a regular cell division pattern and shows eight chromosomes 

 on the mitotic spindle (Fig. AJ, 1 to 8). The second division, then, 

 parallels the first pregametic division found in most other ciliates, 

 with a long-continued prophase (9 to 14) which involves a "para- 

 chute" stage (13). Instead of four tetrads appearing in the metaphase 

 of this division, about thirty-two granules, most of them in pairs, 

 make their appearance (15), and sixteen of them go to each pole (16). 

 During the following division (17 to 20), only eight chromatin 

 bodies show in the prophase (18), but in the metaphase four elon- 



