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FUNDAMENTALS OF CYTOLOGY 



The two animals become united by their ventral sides and the macronucleus 

 of each begins to degenerate, while the micronucleus divides twice to form four 

 spindle-shaped bodies. Three of these degenerate, forming the "corpuscles de 

 rebut," which play no further part. The fourth divides into two, one of which. 



Fk;. 100. — Diagram illustrating nuclear behavior during conjugation in Paramecium. 

 Explanation in text. {From T. H. Morgan, after G. X. Calkins.) 



the "female pronucleus," remains in the body, while the other, or "male pro- 

 nucleus," passes into the other animal and fuses with the female pronucleus. 

 Each animal now contains a cleavage-nucleus equally derived from both the 

 conjugating animals, and the latter soon separate. The cleavage-nucleus in 

 each divides three times successively, and of the eight resulting bodies four 



