SEXUALITY 687 



The same question has been raised by Phihp and Haldane (1939) 

 from an analysis of data in many experiments by Moewus on crossing 

 over and segregation in both Chlamydonionas and Protosiphon. These 

 authors calculated that the chance of getting such close numerical agree- 

 ment among the 22 experiments analyzed was once in 3.5 X 10^^ trials. 

 According to them "if every member of the human race conducted a 

 set of experiments of this type daily, they might reasonably hope for 

 such a success once in 50,000 million years." They suggest that this im- 

 plies a conscious or unconscious adjustment of observations to fit a 

 theory and they call for repetition of the experiments by an independent 

 worker. The failure of Pringsheim and Ondracek (1939) in their at- 

 tempts to confirm certain parts of Moewus's work, their numerous criti- 

 cisms, the criticisms of Philip and Haldane, the internal inconsistencies 

 in Moewus's data, and the great theoretical importance of the work, all 

 make independent repetition of the work an urgent need. 



Sexuality in Paramecium and Other Ciliate Protozoa 



The ciliate Protozoa differ from Chlamydomonas and the flagellates 

 in their nuclear condition and in some features of the sexual phenomena. 

 There are two kinds of nuclei: macronuclei and micronuclei. Ordinarily 

 the macronucleus disappears during the sexual processes and a new one 

 is formed from a product of the micronucleus. The micronuclei alone 

 contain recognizable chromosomes and play the leading role in the 

 nuclear changes involved in sexual processes. The vegetative individuals 

 contain diploid micronuclei that undergo maturation with reduction of 

 the chromosomes to the haploid condition during mating. In each con- 

 jugant two reduced nuclei are formed. In most ciliates, both of these 

 are functional: one remains within the animal in which it is formed and 

 is known as the stationary pronucleus, or gamete nucleus; the other goes 

 into the mate of this animal and is known as the migratory gamete 

 nucleus, or pronucleus. The two nuclei present in each conjugant after 

 exchange of pronuclei unite to form a synkaryon. Conjugation thus in- 

 volves a reciprocal fertilization, both conjugants being fertilized, each 

 by the other. The conjugants then separate and each reconstitutes a new 

 nuclear apparatus and gives rise to progeny by repeated fissions. (See 

 Chapter XII.) 



The mating process is somewhat different in the peritrichous ciliates. 



