Opalina. 299 
describes. This species shows phenomena exactly similar to those 
described for O. intestinalis and O. caudata in the extrusion of the 
vegetative chromatin, the original nuclei persisting as reproductive 
nuclei (Fig. 285, Pl. XX VII; 299—306, Pl. XXVIII). 
It is evident that the number of the chromatin masses in the 
nuclei of the minute Opalinae dimidiatae in the recta of the tad- 
poles is much less than in the larger animals in the frog’s rectum. The 
number of chromosomes seems to be either five or six (Figs. 307—309, 
Pl. XXVIII, indicating ten or twelve chromosomes in the nuclei of 
the full grown forms. I neglected to study this point carefully in 
the nuclei of the living animals and in the acetic-carmine prepora- 
tions last spring, and have not yet worked through my preserved 
material of the gametes of this species, so that the statement of 
the reduced number of chromosomes is based on sketches made 
without that thought especially in mind. There is, however, no 
doubt that the number of chromosomes is reduced. The only doubt 
is as to the exact number present. 
The cysts have from one to seven or more (NERESHEIMER 
twelve) nuclei (Figs. 285—288, Pl. XX VII), and the animals which 
hatch from the cyst have as many (Figs. 289—292, Pl. XXVII; 
299—303, Pl. XXVIII). On this account, as well as because the 
nuclei are less clear, this species is not so favorable for study. 
Macro- and microgametes arise as in the binucleated forms. 
The microgametes are simular to those described for other species, 
their tails sometimes being of very great length (Fig. 310, Pl. XXVIII). 
The true long-tailed microgametes arise by longitudinal division from 
short-tailed forms, as in other species (Fig. 308, Pl. XXVIII). The 
macrogametes, like the full grown individuals in the asexual genera- 
tion, are often rather pointed posteriorly. On this account they 
frequently somewhat resemble the short-tailed mother-cells of the 
microgametes, but the latter can be distinguished by their fewer, 
longer and weaker cilia. 
Copulation occours between uninulecated microgametes and macro- 
gametes which have one or two (or possibly more?) nuclei (Fig. 312, 
Pl. XXVIII). The compound nuclei resulting from fusion are unusually 
large, and they have a characteristic elongated spindle form which 
may indicate division; it is less pointed, however than that seen in 
the division of syncaria in the zygotes of the binucleated species. 
In this species the nuclei are more independent of one another than 
in the binucleated species, not dividing simultaneously but usually 
one dividing while the other remains quiescent (Figs. 315, 316, 
