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GARY N. CALKINS 



of the micronuclei in thirty-one pairs. This comparison was 

 suggested by the possibility of sexual differences in the two indi- 

 viduals forming a pair. The results are tabulated in the accom- 

 panying table: 



It is evident that no constant relation exists between the con- 

 jugating individuals and the number of micronuclei present at 

 the beginning of conjugation. The predominating number is 

 four and the predominating combination is five and four. In 

 all cases one or more is degenerating. In later stages the differ- 

 ences are greater owing to the numbers of degenerating micro- 

 nuclei resulting from the maturation mitoses. 



Not all of the nuclei present at the beginning of conjugation 

 take part in the maturation divisions. The largest number of 

 first maturation spindles seen in any individual is four (fig. 47). 

 and in this case all of the micronuclei participated; but in its 

 mate, only three of five nuclei formed spindles. The fate of 

 these unused nuclei is only conjectural, but they probably de- 

 g;nerate. Nor is there any morphological peculiarity to distin- 

 guish those nuclei which will form spindles from those which will 

 not. It appears to be a matter of position, for the spindles are 

 usually found in the anterior and central parts of the organism 

 while the inactive nuclei are usually in the posterior ends. 



The maturation divisions follow the usual sequence in ciliates, 

 viz., first maturation, second maturation, and third, or pronuclei 



