256 BULLETIN 120. rXlTKD STATES NATIONAL MUSEUM. 



tion of chroniidia witliin the eytoi)lasin of the parent cell, and the 

 ori<rinal nucleus with its retained chromatin derrenerates and is ab- 

 sorbed into tlie cytoplasm. The formation of nuclei in the cytoplasm 

 from chroniidia has recently been shown by Kofoid (1021) to be 

 A erv improbable, to saA' the least. 



In comparison Avith these diverse phenomena in Euciliata and the 

 loAver Protozoa. Avhat do we find in the Opalinidae ? In the Opalinids 

 we find in each nucleus two sorts of chromatin contained in distinct 

 chromosomes. In the Protoopalinas and Zelleriellas the cbnditions 

 are very clear, for the nuclei are laroe and the number of the chromo- 

 somes is small, from 4 to 10. The OpaHnid nucleus has no centro- 

 some. but Ave do find a layered distribution of tlie nuclear contents, 

 similar to that seen in the I*lasmodroma. Just beneath the nuclear 

 membrane lie the large, thin masses of chromatin. Avhich in mitosis 

 form the ribbon-shaped macrochromosomes. A little deeper in the nu- 

 cleus lie the beadlike granules of chronuitin. Avhich in mitosis aggre- 

 gate into lines to form the granular microchromosomes. Still more 

 central are the achromatic granules and films. 



It seems probable that the macrochromatin. peripheral, in Opa- 

 linids is homologous Avith the peripheral chromatin in Plasmodroma ; 

 while the microchroniatin of Opalinids is homologous with the chro- 

 matin of the Plasmoch'ome caryocentrosome; the Opalinid acliroma- 

 tin being hom()k)gous to all the achromatic material of the whole 

 nucleus in Plasmodroma including both that of the caryocentrosome 

 and that of the peripheral zone of the nucleus, leaving out of account 

 of course the plasmatic nucleolus. 



The sexual phases of the life cycle of the Opalinids haA^e not been 

 studied Avith these chromatin distinctions in mind. I had definitely 

 planned to do this before Avriting this paper, but first the war and 

 now other circumstances beyond control have prevented collecting 

 the matei-ial necessary for this study. Previous studies of the sexual 

 and presexual phenomena by Neresheimer (1907) and by myself 

 (1909) and certain observations of LoAventhal (1908) giA^e indica- 

 tion of some of the major relations, 



Xeresheimer described for OpaUna ramniim the degeneration of 

 the nuclei in good-sized individuals. It Avas said that before these 

 nuclei degenerated and were absorbed they gave off into the cy- 

 toplasm great quantities of chromidial material, from Avhich gradu- 

 ally ncAv nuclei Avere formed, at first small, but growing to a larger 

 size. vSome time after this process Avas completed the animals entered 

 upon a period of rapid division, by Avhich they became small and 

 came to contain but fcAv nuclei. These small individuals encysted 

 and. passing out into the Avater, infected the tadpoles which ingested 

 them. I have found from 1 to 12 nuclei in such infection cysts. 

 The nuclei of the cysts I have found to contain each from one to 



