180 SEX IN MICROORGANISMS 



non for Actinophry s sol and certain other Heliozoa, as stated, for 

 example, by Penard (1904b). According to Schaudinn (1896), after 

 plastogamy, individuals of Actinophry s sol separate again without 

 nuclear fusion and without loss of pseudopodia. In addition, Schau- 

 dinn described a process of syngamy, involving first the fusion of two 

 individuals followed by withdrawal of pseudopodia and encystment 

 in a common gelatinous membrane; then a second folded membrane 

 formed about each individual. After this a "reduction" division took 

 place in each cyst, one daughter nucleus migrating to the periphery 

 and condensing into a "polar body." Then fusion of the two haploid 

 cells, including karyogamy, took place. Later the zygote nucleus 

 divided mitotically and two daughter cysts were produced, from each 

 of which a new vegetative individual emerged. 



Schaudinn's account, while similar in general features, varied in 

 detail from the later accounts of Distaso (1908) and Belaf (1923). 

 Distaso described encystment of a single individual followed by 

 division within the cyst producing gametocytes, then two matura- 

 tion divisions, each producing a "polar body." Fusion of the haploid 

 isogametes followed. He called the process autogamy but failed to 

 give details about the chromosomes. Belaf's more complete account 

 (Fig. P) agreed in all general features with that of Distaso, but he 

 counted forty-four chromosomes in vegetative divisions, twenty-two 

 tetrads in the first maturation, and twenty-two dyads in the second 

 maturation division. After maturation short pseudopodia appeared at 

 one end of one of the gametes to initiate the fusion into a diploid 

 zygote (Fig. P, 6 to 8). The zygote formed a more permanent cyst 

 wall, and after a rest period emerged and assumed the active state. 



It may be noted that in one gametocyte the progress of matura- 

 tion was slightly more rapid than in the other (3 to 5). Since the 

 gamete so produced took the initiative in bringing about fertilization, 

 it is regarded as the male. 



Sexual reproduction in Actinophry s sol is essentially similar to 

 that described for Actinosphaeriwn eichhorni by Hertwig (1898). 

 Under certain conditions, such as starvation after being well-fed, mul- 

 tinucleate adults withdrew their pseudopodia and encysted, produc- 

 ing the "mother cyst." About 95 per cent of the contained nuclei 

 degenerated. The cytoplasm within the "mother cyst" then divided 

 into a series of "primary cysts," each containing one of the surviving 

 nuclei. (This primary cyst is comparable to the initial cyst of Ac- 



