Some Problems of Reproduction: a Comparative Study of ...

46 MARCUS M. HARTOG.
The following schema contrasts the conjugation of the
Desmid Closterium, and of a Ciliate.
The zygote of the Closterium is totally different from the
gametes, whose structure can only be obtained afresh by a
very complex reorganisation and after protracted rest. The
Ciliate, on the contrary, carries away from conjugation its
cytoplast with all its complexity retained, and yet has a
nucleus of the same " form " as that of the zygote of Closterium.
The process then seems to involve the suppression
of formation of proper gametes, in order to gain the advantage
of the retention of the cytoplasmic body unchanged.
Fie. 7.—Comparisons of three stages of the processes immediately leading
up to conjugation in Closterium (A) and Paramoecium (B). la each case
two zygote-nuclei of the value (N' + M' = Z) are formed, but the cytoplasts
are unchanged in B, and totally altered in A.
Having found a key to the final processes of conjugation we
can step back, and consider the first two mitoses with the formation
of the rejection-nuclei. We may fairly regard these
also as attempts to form a plurality of gametes comparable
with the processes observed in certain Fucacese, the position
in the cytoplast determining which nuclei shall be rejected.
Possibly, too, the failing energies of the meganucleus at this
stage are insufficient to determine the division of the cytoplast;