154 PROTOZOOLOGY 



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

 of Sphaeromyxa sahrazesi (Fig. 245), 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 

 Endamoeha hlattae. Mercier (1909) believed that in this amoeba 

 there occurs anisogamy soon after excystment in the host's intestine, 

 but this still awaits confirmation. Cultural studies of various para- 

 sitic amoebae in recent years show no evidence of sexual reproduc- 

 tion. Among the Ciliophora, the sexual fusion occurs only in 

 Protociliata (Fig. 263). 



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. 77), two similar individuals come in contact on their 

 oral surface (a). The micronucleus in each conjugant divides 

 twice (h-e), forming four micro nuclei, 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 pronucleus (/, g). The wandering pronucleus in each 

 of the conjugants enters the other individual and fuses with its sta- 

 tionary pronucleus (h, r). The two conjugants now separate from each 

 other and become 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). Cytosomic fision follows then, producing 

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

 duals, each containing a micronucleus and a macronucleus (a). Ac- 

 cording to Jennings, however, of the four smaller nuclei formed in 

 the exconjugant indicated in Fig. 77, o, only one remains active, and 

 the other three degenerate. This active nucleus divides prior to the 

 cytosomic division so that in the next stage {p), there are two de- 

 veloping macronuclei and one micronucleus which divides once more 

 before the second and last cytosomic division (q). During these 

 changes the original macronucleus disintegrates, degenerates, and 

 finally becomes absorbed in the cytoplasm. 



In 1937, Sonneborn discovered that in certain races of P. aurelia, 



I 



