246 SEX IN MICROORGANISMS 



ferently staining chromatids; the more darkly staining male chroma- 

 tids are segregated to one pole and the more lightly staining female 

 chromatids to the other pole by a special mitotic mechanism. 



In the Sarcodina, cell fusions without adequate chromosome data 

 have been described for various members of the Proteomyxa, Amoe- 

 bina and Testacea. In the Foraminifera, syngamy is common, usually 

 alternating with asexual multiple fission. Diploid-haploid sequences 

 have been worked out for a few species. Gametes are amoeboid in 

 some species, flagellated in others. In the Heliozoa, meiosis and ap- 

 proximate isogamy have been reported for Actinosphaerium eich- 

 horni and for Actinophrys sol with full chromosome details described 

 for the latter species. Formation of flagellispores has been reported for 

 various kinds of Radiolaria by several authors, but satisfactory evi- 

 dence for syngamy has not been found. 



In the Sporozoa, sexual reproduction appears to be general. In 

 the Gregarinida both isogamous and anisogamous unions and both 

 pregametic and postzygotic meioses have been described. In the 

 Coccidia and Haemosporidia, anisogamy prevails with postzygotic 

 meiosis the rule in the Coccidia. iMeiosis has not been satisfactorily 

 worked out for the Haemosporidia. Attention is called to evidence 

 indicating that sex determination takes place early in the development 

 of gregarines and coccidia, possibly at the first postzygotic nuclear 

 division. In certain cases, development of a parasite is seen to be 

 correlated with developmental stages of the host. In the Myxospo- 

 ridia, Actinomyxidia, Microsporidia and Haplosporidia, autogamy 

 seems to be the rule, with isogamy or slight anisogamy occurring. 

 No sexual reproduction has been reported for the Hehcosporidia or 

 Sarcosporidia. 



In the Ciliophora, certain members of the Protociliata, all of 

 which are endozoic, are said to show isogamy or anisogamy of gam- 

 etes which are produced by fission of gamonts that excyst in new 

 hosts. In the Euciliata and Suctoria, sexual reproduction commonly 

 takes the form of conjugation during which mutual fertilization takes 

 place between the conjugants. Conjugants are often similar but may 

 be dissimilar in size and morphology. They frequently are smaller 

 than nonconjugants, the result, in some cases at least, of special pre- 

 conjugant divisions. In the Peritricha, conjugants are regularly dis- 

 similar in size, the microconjugant fusing partially or wholly with 

 the macroconjugant, which alone survives. In certain members of the 



