SEX IN PROTOZOA 235 



Differentiation of Conjugants 



Attention has already been called to the regularity with which 

 conjugants of different sizes occur among members of the Peritricha 

 and sometimes also in the Suctoria. Dogiel (1925) believed that con- 

 jugants were generally different, and he offered many tables of meas- 

 urements, mostly in the Ophryoscolecidae, to support the concept. 

 Some later w riters have reported size differences between conjugants, 

 as, for example, in various species of Chilodonella (MacDougall, 1925, 

 1936), Cry ptochihivi echini (Russo, 1926, etc.), Lada tctnishi (Fig. 

 AG, 20; Miyashita, 1928), Fty cbostountm (=Lada) chattoiii (Studit- 

 sky, 1932), Concho phtbirius viytili (Kidder, 1933), and Entorrhi- 

 pidiiivi echini (Yagiu, 1940). According to Enriques (1908) conju- 

 gants of Chilodonella nncinatns did not differ in size until after 

 attachment, and he thought that the contact stimulated size differen- 

 tiation, which he called "hemisex." On the other hand, Ivanic (1933b) 

 denied any sex differences in C cuciillus. In Dogiel's (1925) review 

 some cases wqvq cited where differences between conjugants were 

 still more pronounced. In Opisthotrichiinn jamis, an endozoic ciliate, 

 a single preconjugant division produced a macroconjugant and a 

 microconjugant of different morphology (Fig. AH, 1). However, 

 Dogiel noted that not only would a micro- and a macroconjugant 

 unite (2), but that two macroconjugants might associate together (3). 



Maupas (1889) believed that in most ciliates the conjugants were 

 smaller than non-con jugants and that this reduction in size resulted 

 from one or more special preconjugant divisions. Although this idea 

 has too many exceptions to be a vahd generalization, a considerable 

 number of examples can be found to support it. Special preconjugant 

 divisions have been described or postulated for a number of ciliates 

 including Dileptus gigas (Visscher, 1927), Balantidimn sp. from the 

 chimpanzee (Nelson, 1934), Nyctothenis cordi^ormis (Wichterman, 

 1937), and Fabrea salina (Ellis, 1937). According to Scott (1927), 

 conjugants of Balantidiiivi caviae were always smaller than non- 

 conjugants, and Bogdanowicz (1930) reported the same condition for 

 Loxodes striata. One wonders if these rapid fissions could be stimu- 

 lated by abundance of food, then inhibited by subsequent lack of 

 food, since decline of food after abundance has often been suggested 

 as a stimulus to conjugation. However, Giese (1938) found no regu- 

 lar decline in size before conjugation in Blepharisma undulans, al- 



