270 BULLKXrX 120, UNITED STATER NATIONAL MUSEUM. 



of this sort probably do not occur in any organisms. There is great 

 need of following the presexiial phenomena in some binucleated 

 species of Opalinid, in which the relations are less complicated, and 

 studying exactly and in detail the wdiole series of nuclear phenomena, 

 including especially a study of the trophochromatin and reproduc- 

 tive chromatin. Pending this study we can only say that the undis- 

 puted chromidial phenomena in the Ciliates include absorption into 

 the cytoplasm of the trophochromatin (macronucleus of Euciliates, 

 most or all of the macrochromatin of the Opalinids) and that in 

 some Plasmodroma the nuclei in the presexual phases of the life- 

 cycle similarly eliminate trophochromatin. As already emphasized, 

 the presexual phenomena in Cepedea and Opalina^ described by 

 Neresheimer, and the closely similar phenomena described by Hart- 

 mann for THchonyinpha^ need careful review. 



The less modified Opalinidae, Frotoo'palina and Zelleriella^ re- 

 semble structually the holotrichous Euciliata, except for two fea- 

 tures: 1, the unique nuclear condition of the Euciliates, and 2, the 

 absence of cytostome in the Opalinids. The latter is probably sec- 

 ondary and due to living in the alimentary canal of their host, bathed 

 by liquid, predigested food. As to nuclear structure, the Opalinids 

 do not possess two different sorts of nuclei, but they do have two or 

 more nuclei in all phases of the life history except during game- 

 togamy, and this is a condition which might, with modification, 

 serve as a foundation for such nuclear differentiation as has arisen 

 among the Euciliates. We know no other group of organisms 

 which could so readily lend itself to such further differentation. 

 Two things are necessary to produce a P^uciliate from a l)inucleatod 

 Opalinid : 1, to have the dividing plane in fission pass between the two 

 daughter nuclei of each pair instead of between the two pairs, thus 

 producing a true and permanent rather than a merely temporary 

 binucleated condition, and, 2, to overdevelop the macrochromatin 

 in one of the nuclei and suppress it in the other. 



Among the Flagellates the aberrant genus T richmxyrafha most 

 nearly approaches the Opalinidae in structure. Some of its species 

 resemble Protoofolma in shape and in locomotor organs, being in 

 form an elongated spindle, and being abundantly clothed with fine 

 cilia arranged in longitudinal, sj^iral rows, each cilium with its basal 

 granule, and these granules connected longitudinally in lines by 

 delicate neural fibrillae. The anterior neural centers in Tricho- 

 nympha, near the base of the proboscisliko organ, seem wholly want- 

 ing in the Opalinidae. The cilia of Trichonymplia differ from those 

 of Protoopalina in being inserted along the crests of well developed 

 ridges instead of at the bottom of delicate furrows in the pellicle. 



It seems not improbable that the Opalinidae and Tnchonymphn 

 may have arisen from similar ancestors. At least Tj-iclwnympha 



