620 FERTILIZATION 



ends, the anterior ends pointing in opposite directions. Kidder (1933b) 

 describes the anterior tip of one member of a pair of Anc!Strm?ia isseli 

 uniting asymmetrically with the peristomal groove part way back on its 

 mate, though the two are of equal size. Miyashita (1927) shows that 

 radically asymmetrical union occurs in Lada tanhhi, in which the micro- 

 con jugant, smaller than its mate, attaches its anterior end to the posterior 

 ventral surface of the macrocon jugant. In Kidderia [Conchophthirius] 

 mytili, Kidder (1933a) shows an almost tandum association, with the 

 anterior peristomal region of the slightly smaller member joined by a 

 wide protoplasmic bridge to the aboral surface of the larger member 

 of the pair. In Dileptus gigas (Visscher, 1927) fusion takes place along 

 the ventral surfaces of the proboscides, and the mouth remains in evi- 

 dence during the entire period of conjugation. 



The varied methods of joining of the conjugants suggest that the 

 location of the fusion bridge is not significant. If ciliate conjugation 

 evolved from a process similar to pseudoconjugation as seen in present- 

 day gregarines, as many protoologists believe, it seems reasonable that 

 one location would serve as well as another, provided the cortex were 

 not too firm for a protoplasmic bridge to be formed. It is interesting 

 in this connection to observe that in Euplotes patella (Turner, 1930), 

 which has a rigid cuirass, no true cytoplasmic bridge is formed. The 

 wandering pronucleus of one conjugant breaks out of the left anterio- 

 ventral margin of the one conjugant and passes backwards through a 

 tube formed by the local separation of the applied surfaces of the two 

 conjugants, and finally enters the cytostome of the other conjugant. This 

 method of entering the apposed conjugant probably developed simply 

 because it was easier to penetrate the soft cytostomal membrane than 

 the rigid cuirass. The mouth-to-mouth migration of the male pronucleus 

 in Cycloposthium bipalmatum (Dogiel, 1925) is a simpler example of 

 the same process. 



In Polyspira and other members of the Foettingereidae, there occurs 

 a remarkable combination of conjugation, fission, and chain formation 

 called "syndesmogamie" by Minkiewicz (1912), and recently renamed 

 "zygopalintomie" by Chatton and Lwoff (1935) in their comprehensive 

 work on the Apostomea. The two conjugants unite by their lateral sur- 

 faces rather than by the usual ventral method, then proceed to undergo 

 a series of synchronous, partial, transverse divisions, until a chain of con- 



