208 SEX IN MICROORGANISMS 



host constitutes a necessary stimulus to further development. Yet the 

 well-known development of micro- and macrogametes of Haemos- 

 poridia from warm-blooded hosts when blood containing the game- 

 tocytes is drawn and reduced to "room" temperature suggests that 

 mere reduction in temperature induces gamete formation. However, 

 we have the definite circumstance, in these two-host parasites, that 

 transfer to an alternate host is required for the life cycle to continue. 

 Whether the host influences are in the nature of "hormones" or other 

 specific substances is yet to be determined. It is possible that the rela- 

 tion between the molting hormone of the wood-feeding roach and 

 the sexual activities of its contained flagellates is unique. 



SUBPHYLUM CILIOPHORA 



The Subphylum Ciliophora is divided into two classes, the 

 Cihata and the Suctoria. Class Ciliata contains Subclass Protociliata, in 

 which there are two or more similar nuclei in each animal, and Sub- 

 class Euciliata, in which each animal has one or more macronuclei 

 and one or more micronuclei. All the Protociliata are endozoic, mostly 

 in the large intestine of Amphibia. Sexual phenomena in cihates have 

 been reviewed by a number of writers, more recently by Diller 

 (1940a), Turner (1941), and Finley (1946). 



Subclass Protociliata 



According to Neresheimer (1907), the life cycle of Opalina 

 ranarum and O. dimidiata includes binary fission through most of 

 the year. In the spring, cysts are formed which pass into the water 

 of breeding pools to be taken up by a new generation of tadpoles, 

 in which sexual reproduction takes place. Similar uninucleate gametes 

 fuse in pairs to produce zygotes which become encysted. When the 

 zygotes excyst, they develop into adults in the new host. Metcalf 

 (1908) confirmed most of this life cycle for Opalina (Protoopalina) 

 caudata, O. (P.) intestinaUs and O. dimidiata, except that he found 

 the gametes to be different in size and failed to confirm the encyst- 

 ment of the zygote. Valkanov (1934) also found anisogamy. Figure 

 Y shows diagrammatically the life cycle of Opalina rananim as 

 illustrated by Prenant (1935) and based on the work of Zeller (1877) 

 and KonsulofF (1921). None of the authors mentioned above gave 



