SEX IN PRO 1 OZOA 247 



Clionotricha and of the Suctoria, complete fusion of conjugants takes 

 place to produce a single synconjugant. Other variations in conjuga- 

 tion include cytogamy (autogamy in each conjugant) and partheno- 

 genesis in each member of a pair. Single individuals may undergo 

 autogam\'. Nuclear reorganization without sexuality may also take 

 place as in endomixis, hemixis and macronuclear reorganization. For- 

 mation of a brood of small gametes by a single parent, as in Dallasia 

 froiitiitii (and other evidence), suggests that conjugation has evolved 

 from a brood-forming ancestral condition. 



It is a pleasure to acknowledge my indebtedness to Dr. J. Russel Gabel 

 for his care and skill in redrawing illustrations from the literature. Acknowl- 

 edgment of sources is made in connection with the individual illustrations or 

 groups. The Wistar Institute kindlv granted permission to use or copy the 

 illustrations in Figs. F, G, H, I, J, K, L, M, S, U, W, AA, AB, AC, AD (1, 2, 

 4), AE (1 to 12), AK, and AM. 



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