Opalina. 303 
their extrusion from the nuclei, is the fact that we often find three 
of these spheres, and that very likely but one is formed in some 
cases. When only one is seen, it may be, of course, that another 
was present but has already been extruded. 
It may be well to note, before leaving this subject, that, in 
Opalina, each nuclear division is associated which a division of the 
cell. The phenomena in Paramaecitum seem less primitive, two cell- 
divisions being suppressed during maturation, and as a consequence 
three nuclei in each gamete degenerating. In Opatina all the cells 
produced by the divisions preceeding copulation are functional 
gametes as in the spermatogenesis of Metazoa. Doubtless the con- 
ditions in the maturation of the eggs of Metazoa and in Paramaecium 
are secondary. 
Relationships of Opalina. 
There seems no ground for doubting the close relationship of 
the several species of Opalina. Possibly the binucleated species 
should be placed in one genus and the multinucleated species in 
another genus. The character of the nuclei, as well as their num- 
ber, is somewhat different in the two groups. It seems, however, 
better to retain the genus as at present constituted and to recog- 
nise the binucleated species as a rather distinct subgenus. 
The connection of Opalina with the Ciliata has recently been 
questioned by NerREsHEIMER (1906 and 1907) who concludes, on the 
basis of the method of reproduction by gametes, that Opalina is 
more nearly related to the Plasmodroma than to the Ciliophora. I 
find myself unable to agree with this suggestion. The cilia with 
their basal granules, and the manner of the arrangement of the 
cilia in spiral rows, so exactly agree with what we see in Ciliata, 
and these organs are so highly developed, that their independent 
origin in two distantly related groups should not be assumed without 
convincing evidence. The resemblance between the excretory or- 
gans in Opalina and Hoplitophrya suggests relationship, and the excre- 
tory organ of Pycnothrix monocystoides (ScHUBOTZ 1908) shows still 
closer resemblance. The presence of a macronucleus containing re- 
fractive spherules in Hoplitophrya makes this form a good transition 
between Opalima and other Ciliata. The frequent fragmentation of 
the macronucleus in Hoplitophrya, without connection with conjugation, 
is again a character somewhat intermediate between higher Ciliata 
and Opalina in which chromatin spherules are formed in the nucleus 
during each mitosis and are dissolved and extruded into the cytoplasm. 
