298 M. M. Mercaur 
Phenomena in other species. 
Opalina caudata. 
In O. caudata all the phenomena are like those described in 
O. intestinalis, except that the reduced number of chromosomes in 
the gametes is three instead of four (Figs. 249, 250, Pl. XXVI), 
as one would expect from the fact that in the nuclei of full-grown 
individuals there are six chromosomes. Compare Fig. 248, Pl. XX VI, 
in which each nucleus is in an early stage of mitosis showing 
twelve chromosomes ready to arrange themselves in double rows 
preparatory to migration to the poles. Compare also Figs. 81 and 82, 
Pl. XX, which represent anaphases and a telophase in mitosis, the 
number of chromosomes being clearly six. 
The cysts have either one or two nuclei (Figs. 252—255, Pl. X XVI), 
and these show the characteristic chromatin spheres which are 
thrown off in the process of getting rid of the vegetative chromatin 
(Figs. 252—254). The gametes and the manner of their formation, 
and the external and nuclear phenomena of copulation are similar 
to what has been described. (See Figs. 257, Pl. XXVI, to 276, 
Pl. XXVII. Observe especially the number of the chromosomes in 
Figs. 273—276.) I have not, however, followed the nuclear pheno- 
mena in the zygotes to quite so late a stage as in O. itestinalis. 
Fig. 276, Pl. XXVII, shows the only instance I have seen of the 
apparent copulation of equal gametes. The drawing is from an 
acetic-carmine preparation and I do not know what would have been 
the later behaviour of the animals. 
Large chromatin spheres, ready for extrusion from the nuclei, 
are shown in Fig. 251, Pl. XXVI, in a rather small individual from 
the rectum of an adult Bombinator pachypus. 
Opalina dimidiata. 
In O. dimidiata, which is a multinucleated species, the earlier 
phenomena are somewhat different. The nuclei are not so easy to 
study, for they are small and the number of chromosomes is greater, 
apparently twelve in the full-grown forms. The chromatin is gener- 
ally arranged in numerous granules just beneath the nuclear mem- 
brane, giving a very characteristic appearance (Figs. 277—280, 
Pl. XXVII). I find no evidence of degeneration of nuclei, or of 
formation of new nuclei from reproductive chromidia, as NERESHEIMER 
