SEX IN PROTOZOA 231 



into single individuals. Most of the material in the niicroconjugant 

 enters the niacroconjugant, but a remnant (10) is cast off. In the case 

 of Opistbo/iectii hcnuevi^uyl, a free-swimming vorticeUid (Fig. AG 

 19), the niicroconjugant fused completely with the macroconjugant 

 (Rosenberg, 1940). 



In the Urceolariidae, which are free-swimming commensals on 

 or in various hosts, the difference in size between conjugants is not 

 so marked as for the sedentary vorticellids. The most recent accounts 

 are those for Ti'ichodma spheroidesi (Padnos and Nigrelli, 1942) and 

 for Urceolaria synaptae (?) (Colwin, 1944). Padnos and Nigrelli 

 reported only two preliminary micronuclear divisions in the micro- 

 conjugant, whereas Colwin recorded three. Colwin found that ex- 

 change of pronuclei sometimes took place before nuclear material of 

 the niicroconjugant passed over into the macroconjugant, leaving a 

 remnant which was later discarded. In Trichodina spheroidesi the 

 usual postconjugant development took place, eight nuclei being de- 

 rived from the snycaryon, seven of which became macronuclei and 

 one the micronucleus. In Urceolaria syjiaptae, however, only four of 

 the eight products of the syncaryon became macronuclei, three de- 

 generated, and one became the micronucleus, following the pattern 

 for Faraniecium caiidatwn instead of that characteristic for vorti- 

 cellids. 



According to Awerinzew (1936), in a species of Lagenophrys, 

 which lives in a lorica on the gill plates of a freshwater crab, Tel- 



FiG. AG. 



1-16, conjugation in Vorticella inoiiilata, from Maupas (1889). 1, niicroconjugant 

 attaching to macroconjugant; 2, first pregametic micronuclear division in niicro- 

 conjugant, break-up of macronucleus; 3, first pregametic division in macroconjugant, 

 second in niicroconjugant; 4, second pregametic division in macroconjugant, third in 

 niicroconjugant; 5, products of these divisions; 6, single nucleus left in each con- 

 jugant after others have degenerated; 7, 8, final pregametic division to produce 

 pronuclei; 9, passage of one pair of pronuclei into macroconjugant where syncaryon 

 is formed; 10, division of syncaryon, small remnant of microconjugant; 11, second 

 postzygotic division; 12, third postzygotic division; 13, eight products from syncar- 

 yon; 14, seven products become macronuclear anlagen, one becomes the micro- 

 nucleus; 15, 16, after first postconjugant cell division. Further divisions segregate 

 anlagen into single cells. 17, 18, Vorticella microstoma, from Finley (1943). 17, divi- 

 sion of a neutral individual into one micro- and one macroconjugant; 18, three 

 microconjugants attached to one macroconjugant. 19, conjugation of macro- and 

 microconjugants of Opistbonecta benneguyi, from Rosenberg (1940). 20, conjugants 

 of unequal size in Lada tanishi, from Aliyashita (1928), with unusual points of con- 

 tact. (All illustrations redrawn.) 



