THE OPALINID CILIATE INFU30RIANS. 255 



the contrary, the plane of division, both in longitudinal and in trans- 

 verse fission, separates the two old nuclei, so that each daughter cell 

 receives the whole of one of the old nuclei, and the binucleated con- 

 dition has to be reestablished by the prompt division of this nucleus 

 into two. The Opalinid condition seems more archaic, the Euriliate 

 condition more advanced. 



Thus far we have discussed chiefly numerical relations in the 

 nuclear conditions of the Opalinidae. The structural and physio- 

 logical phenomena also are noteworthy. In many Protozoa we can 

 distinguish two sorts of chromatin, which have been called tropho- 

 chromatin and idiochromatin, or nutritive and reproductive chro- 

 matin. In the Euciliata one nucleus, the larger, has the nutritive 

 chromatin greatly developed, leaving, so far as we can see, no un- 

 modified reproductive chromatin present. In the small nucleus, on 

 the other hand, we do not demonstrate the presence of any specialized 

 trophochromatin. All seems to be idiochromatin. Apparently 

 trophochromatin is derived from idiochromatin, being, in different 

 organisms, more or less hypertrophied and modified in connection 

 with its role in metabolism. 



In many of the less modified Protozoa, which have centro-nuclei, 

 the nuclear centrosome not only contains achromatic kinetoplasm, 

 but also usually is very rich in chromatin. Outside this nuclear 

 chromocentrosome. in the peripheral layer of the nucleus, we find 

 other chromatin. In some species the peripheral chromatin seems 

 clearly to arise from the chromocentrosome, granules of chromatin 

 arising in this central body and passing out into the peripheral 

 region of the nucleus. We have by no means sufficient evidence to 

 indicate that in all species the chromatin of the peripheral layer is 

 of chromocentrosomal origin. In the mitoses of some of these 

 lower Protozoa we find two distinct sets of chromosomes, one set 

 derived from the chromatin in the chromocentrosome, another set 

 derived from the chromatin of the peripheral region of the nucleus. 

 In some species, at least, these two sets of chromosomes remain dis- 

 tinct throughout the whole mitotic cycle, the centrochromatin going 

 to the caryocentrosomes of the daughter nuclei, the peripheral 

 chromatin remaining peripheral in the daughter nuclei. More study 

 is needed of these phenomena. We do not know enough of the rela- 

 tion of these two groups of chromatin to the chromidia that in so many 

 Protozoa are said to pass out from the nucleus into the cytoplasui. 

 Schandinn and others have shown that in numerous forms the 

 chromidia are trophic, and that at the time of sexual reproduction 

 these vegetative chromidia are absorbed, the residual chromatin in 

 the nucleus functioning as the orderly carrier of inheritance in the 

 regulated series of sexual phenomena. On the other hand, in other 

 species, the nuclei of the gametes are said to be formed by aggrega- 



