22 BULLETIN" 120, UNITED STATES NATIONAL MUSEUM, 



occur in each species in full-sized individuals, so the}' must consid- 

 erably precede in time the sexual phenomena in the Opalinids in the 

 tadpole. I am in doubt as to the interpretation of these phenomena. 

 They seem to indicate pathological nuclear degeneration, perhaps 

 associated with nuclear parasites, or they may possibly be normal 

 phases of the life history, as Neresheimer described. There is need 

 of careful restudy of the life history to determine the exact phe- 

 nomena here. Figures 98, 5, 99, e, and 100, c, show cells whose origi- 

 nal nuclei are in active division, apparently indicating normal con- 

 dition, though the cytoplasm contains numerous smaller nuclei. On 

 the other hand, figures 99, c and /, show original nuclei which are 

 not in normal, or at least in usual, condition, the nuclear contents 

 having aggregated to form one or two granular spheres which some- 

 what resemble the small nuclei in the cytoplasm. 



In Protoopalina intestinalis the further phenomena observed are 

 as follows: A short time (about four generations) previous to 

 encystment the nuclei of the already small Opalinids show a change 

 and instead of eight massive chromosomes have but four (fig. 9). 

 The significance of this change is not certain, but it may be synapsis 

 which has occurred. Thereafter, until the macrochromatin is thrown 

 away before copulation, the macrochromosome number in the nuclei is 

 uniformly four. 



During encystment, or immediately preceeding or following it, 

 one sees in each nucleus, whether of binucleated or uninucleated in- 

 dividuals, from one to four, usually one to three, balls of densely 

 staining chromatin in addition to the chromatin granules in the 

 nucleus (fig. 5, <z, 5, c, and d). Tlijese chromatin balls are ex- 

 truded from the nucleus into the cytoplasm and there are absorbed 

 (fig. 5, e and /) . Later, when the cysts have hatched in the tadpole, 

 we find the small Opalinids with four chromosomes in their nuclei. 

 The phenomena have not yet been so followed as to enable us to 

 say whether these persistent chromosomes are formed from the chro- 

 matin granules or from the chromatin masses, though there is con- 

 siderable indication that the massive chromosomes are thrown bodily 

 out of the nucleus, having first massed together to form the chro- 

 matin balls described above. Such absorption into the cytoplasm 

 of masses of chramatin before sexual reproduction is apparently 

 comparable to the disintegration and absorption of the meganucleus 

 in Paramecium and other Euciliates. In some of my former experi- 

 ments upon Protoofolina intestinalis I fed small Opalinids, as well 

 as cysts, to the tadpoles. These small Opalinids passed apparently 

 unharmed through the intestine into the rectum of the tadpole. 

 Then, however, they began to throw off great masses of chromatin 

 from their nuclei into the cytoplasm (fig. 10). The pictures ob- 



