156 PROTOZOOLOGY 



to feel that if an animal does not happen to meet another indi- 

 vidual in the same physiological condition as itself, its reorga- 

 nizing 'urge' will be expressed by autogamy, as a substitute for 

 conjugation." 



The paedogamy occurs in at least two species of Myxosporidia, 

 namely, Leptotheca ohlmacheri (Fig. 212) and Unicapsula 

 muscularis (Fig. 213). The spores of these Myxosporidia contain 

 two uninucleate sporoplasms which are independent at first, but 

 prior to emergence from the spore, they undergo a complete 

 fusion to metamorphose into a uninucleate amoebula. Perhaps 

 the classical example of the paedogamy is that which was found 

 by Hertwig (1898) in Actinosphaeriiim eichhorni. The organism 

 encysts and the body divides into numerous uninucleate second- 

 ary cysts. Each secondary cyst divides into two and remains 

 together within a common cyst-wall. In each the nucleus divides 

 twice, and forms four nuclei, one of which remains functional, 

 the remaining three degenerating. The paedogamy results in 

 formation of a zygote in place of a secondary cyst. Belaf (1922) 

 observed a similar process in Adinophrys sol (Fig. 78). The helio- 

 zoan withdraws its axopodia and divides into two uninucleate 

 bodies which become surrounded by a common gelatinous en- 

 velope. Both nuclei divide twice and produce four nuclei, three 

 of which degenerate. The two daughter cells, each with one 

 haploid nucleus, undergo paedogamy and the resulting individual 

 now contains a diploid nucleus. 



Endomixis. Woodruff and Erdmann (1914) observed that in 

 Paramecium aurelia (Fig. 79) at regular intervals of about 30 

 days, the old macronucleus breaks down and disappears, while 

 each of the two micronuclei divide twice, forming eight nuclei. 

 Of these, six disintegrate. At this point the organism divides 

 into two, each daughter individual receiving one micronucleus. 

 This nucleus soon divides twice into four, two of which develop 

 into macronuclei, and the other two divide again. Here the 

 organisms divide once more by binary fission, each bearing one 

 macronucleus and two micronuclei. This process which is "a com- 

 plete periodic nuclear reorganization without cell fusion in a 

 pedigreed race of Paramecium" was called by the two authors 

 endomixis. In the case of P. caudatum, they found endomixis 

 occurs at intervals of about 60 days. Sonneborn (1937) succeeded 

 in inducing endomixis in certain stocks of P. aurelia by placing 



