SPIROSTOMUM AMBIGUUM 423 



apparent that the conjugants were all at the final stage of 

 growth when division should commence. No information 

 throwing light on the means by which the smallness in size in 

 the conjugants is arrived at, was obtained. In his biometrical 

 study of conjugation in Paramoecium cau datum 

 Dr. Eaymond Pearl (22) found ' that conjugant individuals 

 when compared with non-conjugants were shorter and narrower 

 and less variable both in length and breadth '. He also showed 

 that there was a high degree of correlation between the lengths 

 of the two members of conjugant pairs. He proved, by 

 numerous careful measurements, that such a high degree of 

 homogamic correlation was not due to the random pairing of 

 individuals in a ' homogeneous population of low variability '. 

 Miss Watters (30) has obtained similar results with regard to 

 the relationship in size between conjugants and non-conjugants 

 in B 1 e p h a r i s m a u n d u 1 a n s . Such rough observations as 

 have been made during the present study of conjugation 

 seem to indicate that similar relationships exist between the 

 conjugants themselves and between the conjugants and the 

 non-conjugants in cultures of Spirostomum ambiguum. 



Both conjugants are, as was noticed by Stein (28), attached 

 along the peristomial groove. This makes the taking in of 

 food during conjugation impossible. From the fact that 

 conjugants, even in the earliest stages of conjugation, are 

 rarely found containing ingested food, it would appear that 

 ingestion ceases some time prior to conjugation. 



The peristomial membranellae are not absorbed during con- 

 jugation. Generally the anterior end of one individual of 

 the pair is attached to a point a little posterior to the anterior 

 end of the peristomial groove of the other. The attachment 

 ends at the cytostome. Since the cytostome is central in posi- 

 tion, it follows that conjugating individuals are attached for 

 half the body-length. Stein (28) in his figure of a pair of con- 

 jugants depicts them as being attached to one another from 

 the extreme anterior end of each. Quite a number of pairs 

 attached in this way have been met with during the present 

 observations, but the method of attachment in the majority 



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