Opalina mitotica, | 89 
dition of Opalina can be changed to a real binucleated condition 
only by the complete suppression, not the mere delay, of one divi- 
sion of the body. Were this to occur, then a transverse division of 
the body, such as we occasionally find, would bisect the two nuclei, 
being not a delayed division belonging to the last mitosis, but the 
division which properly belongs with the present mitosis of the 
two nuclei (Fig. A, c. We can conceive the same result as 
following still longer delay in the postponed division of the body, 
it not occuring until the two dauehter nuclei are separated to a 
considerable distance, so that the division of the body (transverse 
in this case) could easily pass between the daughter nuclei, pro- 
ducing thus in each daughter cell a truly binucleated condition. 
“It seems to me quite probable that such has been the history 
of the evolution of the binucleated condition in higher Ciliata: first 
delay in division of the body, establishing a temporary binucleated 
condition; then complete suppression of this delayed division of the 
celi-body, establishing a true binucleated condition, each nucleus, as 
apparently now in Paramoecium, belonging to a potentially, but not 
actually, independent individual. 
“The truly binucleated forms, as well as the falsely binucleated 
Opalinae, are really potentially double individuals; and similarly 
the multinucleated Opalinae, arising by further temporary suppression 
of divisions of the body, are highly compound forms composed of many 
potential individuals. These individuals all become ultimately distinct 
before or in connection with copulation, even in the multinucleated 
Opalinae, the temporarily suppressed divisions of the body finally 
appearing rapidly in the spring and producing unicellular gametes.” 
The tendency to assume a multinucleate condition is not restrieted 
to the Opalinas alone among the Cikiata; there are several species 
which, at least under certain conditions, are multinucleate, e. g. 
Loxodes rostrum and the form recently described by Power’s and 
MITCHELL, Paramoecium multimieronucleata. 
The most striking peculiarity in ©. mitotica is the one from 
which I have named the species, namely the fact that its nuclei 
“rest” in the midst of mitosis, their chromatin showing a late ana- 
phase condition and not forming a network or being in scattered 
granules. I know of no other animal or plant of which this is true. 
Why should all other nuclei “rest” with their chromatin in a granular 
or network condition? Why should mitosis in all other species, 
when entered upon, be promptly completed? Is it merely that the 
