86 Maynarp M. METCALF, 
a new macronucleus by metamorphosis of a micronucleus than to 
carry the highly specialized and hypertrophied macronucleus through 
the stages of conjugation. On the other hand in the Opalinas the 
transient character of the binucleate condition does not allow any 
such divergence and specialization in the nuclei. The Opalinas have 
not developed micronuclei and macronuclei, but each nucleus is an 
ordinary unspecialized nucleus. In a previous paper I have written 
upon this subject as follows (MErTcArr, 1909, p. 272): “The question 
as to what in Opalina is the full homolog of the macronucleus in 
higher Oiliata can best be approached through a discussion of the 
evolution of the condition with two functionally diverse nuclei. The 
macronucleus of higher Ciliata arises by the metamorphosis of a 
nucleus which has itself arisen by division from the micronucleus. 
It is therefore phylogenetically a complete nucleus and not a mere 
mass of granules extruded from a nucleus and gathered into a group. 
The macronucleus seems to be specialized in connection with the 
nutrition of the cell. It is able to divide, as does the micronucleus, 
in the vegetative divisions of the cell, but it takes no part in the 
special phenomena, interpreted as maturation, which precede con- 
jugation. The micronucleus apparently holds in abeyance the func- 
tions connected with the nutrition of the cell, but the potentiality 
of these functions must be present, since daughter nuclei from the 
mieronuclei are able to transform into macronuclei. Probably each 
type of nucleus is a complete nucleus, the nucleus especially connec- 
ted with conjugation being slightly specialized by diminution of 
some of its funetions and probably of the chromatic material upon 
which these functions rest. The the macronucleus is specialized by 
the great development of its nutritive activities and a corresponding 
great increase in the amount of chromatin especially associated with 
these functions. The specialization and hypertrophy of the macro- 
nucleus seems to have gone so far that it is difficult to secure con- 
jugation of the macronuclei, and so, partly as a consequence, the 
macronuclei degenerate. The germinal (unspecialized) chromatin is 
so overbalanced by nutritive (specialized) chromatin in the macro- 
nuclei that it is unable to assert itself and bring about conjugation 
of these nuclei, and without occasional readjustment such as is se- 
cured through conjugation, ultimate degeneration seems unavoidable. 
“Before copulation or conjugation there seems to be quite gene- 
rally, among. the Protozoa at least, a process of reestablishing the 
proper balance of the nutritive and other chromatin in the nucleus. 
