REPRODUCTION 187 



dium vivax (Fig. 256), anisogamy results in the formation of the 

 ookinetes or motile zygotes which give rise to a large number of 

 sporozoites. Among Myxosporidia, a complete information as to 

 how the initiation of sporogony is associated with sexual reproduc- 

 tion, is still lacking. Naville, however, states that in the trophozoite 

 of Sphaeromyxa sabrazesi (Fig. 277), micro- and macro-gametes 

 develop, each with a haploid nucleus. Anisogamy, however, is pe- 

 culiar in that the two nuclei remain independent. The microgametic 

 nucleus divides once and the two nuclei remain as the vegetative 

 nuclei of the pansporoblast, while the macrogamete nucleus multi- 

 plies repeatedly and develop into two spores. Anisogamy has been 

 suggested to occur in some members of Amoebina, particularly in 

 Endamoeba blattae (Mercier, 1909). Cultural studies of various para- 

 sitic amoebae in recent years show, however, no evidence of sexual 

 reproduction. Among the Ciliophora, the sexual fusion occurs only 

 in Protociliata (Fig. 294). 



Conjugation. The conjugation is a temporary union of two indivi- 

 duals of one and the same species for the purpose of exchanging part 

 of the nuclear material and occurs almost exclusively in the Euci- 

 liata and Suctoria. The two individuals which participate in this 

 process may be either isogamous or anisogamous. In Paramecium 

 caudatum (Fig. 83), the process of conjugation has been studied by 

 many workers, including Biitschli (1876), Maupas (1889), Calkins 

 and Cull (1907), and others. Briefly the process is as follows: Two 

 similar individuals come in contact on their oral surface (a). The 

 micronucleus in each conjugant divides twice (b-e), forming four 

 micronuclei, three of which degenerate and do not take active part 

 during further changes (f-h). The remaining micronucleus divides 

 once more, producing a wandering pronucleus and a stationary pro- 

 nucleus (/, g). The wandering pronucleus in each of the conjugants 

 enters the other individual and fuses with its stationary pronucleus 

 (h, r). The two conjugants now separate from each other and be- 

 come exconjugants. In each exconjugant, the synkaryon divides 

 three times in succession (i-m) and produces eight nuclei (n), four 

 of which remain as micronuclei, while the other four develop into 

 new macronuclei (o). Cytoplasmic fision follows then, producing 

 first, two individuals with four nuclei (p) and then, four small in- 

 dividuals, each containing a micronucleus and a macronucleus (a). 

 Jennings maintained that of the four smaller nuclei formed in the 

 exconjugant (o), only one remains active and the other three de- 

 generate. This active nucleus divides prior to the cytoplasmic divi- 



