204 PROTOZOOLOGY 



different cells, then paedogamy. The autogamy is of common occur- 

 rence in the myxosporidian spores. The young sporoplasm contains 

 two nuclei which fuse together prior to or during the process of ger- 

 mination in the alimentary canal of a specific host fish, as for exam- 

 ple in Sphaeromyxa sabrazesi (Figs. 276; 277) and Myxosoma cato- 

 stomi (Fig. 275). In the Microsporidia, autogamy appears to initiate 

 the spore-formation at the end of schizogonic activity of individuals 

 as in Thelohania legeri (Fig. 76). 



Diller (1936) observed in solitary Paramecium aurelia (Fig. 89), 

 certain micronuclear changes similar to those which occur in 

 conjugating individuals. The two micronuclei divide twice, form- 

 ing eight nuclei (a-d), some of which divide for the third time (e), 

 producing two functional and several degenerating nuclei (/). The 

 two functional nuclei then fuse in the "paroral cone" and form the 

 synkaryon (g, h) which divides twice into four (i, j). The original 

 macronucleus undergoes fragmentation and becomes absorbed in the 

 cytoplasm. Of the four micronuclei, two transform into the new 

 macronuclei and two remain as micronuclei (k) each dividing into 

 two after the body divided into two (Z). 



Another sexual process appears to have been observed by Diller 

 (1934) in conjugating Paramecium trichium in which there was 

 no nuclear exchange between the two conjugants. Wichterman 

 (1940) observed a similar process in P. caudatum and named it cytog- 

 amy. Two small (about 200/x long) individuals of P. caudatum 

 fuse on their oral surfaces. There occur three micronuclear divisions 

 as in the case of conjugation, but there is no nuclear exchange be- 

 tween the members of the pair. The two gametic nuclei in each indi- 

 vidual are said to fuse and form a synkaryon as in autogamy. Sonne- 

 born (1941) finds the frequency of cytogamy in P. aurelia to be cor- 

 related with temperature. At 17°C, conjugation occurs in about 95 

 per cent of the pairs and cytogamy in about 5 per cent; but at 10° 

 and 27°C, cytogamy takes place in 47 and 60 per cent respectively. 

 In addition, there is some indication that sodium decreases and 

 calcium increases the frequency of occurrence of cytogamy. 



The paedogamy occurs in at least two species of Myxosporidia, 

 namely, Leptotheca ohlmacheri (Fig. 279) and Unicapsula muscularis 

 (Fig. 280). The spores of these myxosporidians contain two uninu- 

 cleate sporoplasms which are independent at first, but prior to 

 emergence from the spore, they undergo a complete fusion to meta- 

 morphose into a uninucleate amoebula. Perhaps the classical exam- 

 ple of the paedogamy is that which was found by Hertwig (1898) in 

 Actinosphaerium eichhorni. The organism encysts and the body di- 



