698 SEXUALITY 



pair both gave rise to cultures in which conjugation took place. Never- 

 theless, Kimball found that the two members of a split pair were always 

 of diverse mating types at the time they conjugated: one was type I, the 

 other type II. Hence such caryonides are unstable in mating type. The 

 type changes back and forth repeatedly; but when conjugation occurs, it 

 is alw^ays between animals of different mating type. 



In the Vorticellidae, the invariable morphological and functional dif- 

 ference between conjugants has already been mentioned. Finley (1939a, 

 1939b) shows clearly that both types of conjugants not only arise within 

 a caryonide, but at a single unequal cell division. The macroconjugant 

 and the microconjugant produced at this fission can then copulate with 

 each other or with other similarly differentiated conjugants of the same 

 caryonide. Here it is obvious that conjugation within a caryonide is never- 

 theless invariably between different mating types or sexes. 



There are, however, a number of known instances of conjugation 

 within a caryonide which require further investigation. Foremost among 

 these are species, without morphological difference between the conju- 

 gants, in which conjugation regularly occurs within a clone or a caryo- 

 nide. This has been reported as common in P. juultiniicronncleatuni by 

 Giese (1938, 1939), less common in P. caudatum by Oilman (1939), 

 and very rare in P. huvsavid by Jennings ( 1938a, 1938b, 1939a, 1939b) . 

 An especially interesting situation is reported for Euplotes by Kimball 

 (1939c). Fluid from a culture of one mating type, added to a culture 

 of a different mating type, induces the latter to conjugate among them- 

 selves. Likewise, in mixtures between normal animals of one mating 

 type and double animals of another type, some of the resulting con- 

 jugant pairs are unions of singles with singles, a few are doubles with 

 doubles, though most are, as would be expected, singles with doubles. 

 The relations here raise the question of whether subjection to fluid from 

 another mating type makes animals acquire a type corresponding to the 

 fluid, as JoUos (1926) showed happens in the alga Dasycladus. If so, 

 it may be difficult or impossible to analyze it satisfactorily, because in 

 ascertaining the types of members of split pairs they have to be sub- 

 jected to the very fluid that would change their type. This may be one 

 of those exasperating problems, like attempting to determine the posi- 

 tion and the velocity of an electron at the same time, in which the meth- 

 ods of investigation essentially alter the things being investigated. 



