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

58 • MARCUS M. HARTOG.
asexual spores in Archegoniate Cryptogams. Hence we may
be allowed to conjecture that the reduction also takes place
in the latter group ; and, by parity, that it is not confined
to gametogonia, but will be found in all mothercells
destined by multiple fission to give birth to a
brood of reproductive cells. In that case the return to
the normal number of chromatomeres would necessarily be
effected by the slow process of nutrition in asexual spores
or their offspring, instead of by the direct process of
summation in the case of gametes. This would give a clear
insight into the action of karyogamy in bringing about rapid
and complete rejuvenescence.
The question of the individuality of the chromatomeres and their persist,
ence, as maintained by Boveri and Rabl, should find its treatment here ; but
I have not yet completed a research bearing on this point. I therefore confine
myself now to the statement that, with Hertwig, I believe the evidence
very inadequate for the support of the theory that the chromatomeres have
distinct and persistent individualities. Professor Strasbiirger has written me
a letter to the same effect, though he had advocated Rabl's views in his
' Kern- und Zelltheilung.'
B. On the Reproductive Incapacity of Obligatory
Gametes.
The reproductive incapacity of gametes is no exceptional
phenomenon among cells, nor is it brought about only in the
differentiation of gametes. It occurs in other cases throughout
the Metaphytes and Metazoa, and we have instances of
its existence as low down as the Colonial Flagellates. In the
genus Volvox all the numerous cells of the colony other than
the few ''germinal cells" (parthenogonidia, oogonia, or spermatogonia),
perfect flagellates equipped with eye-spot, contractile
vacuoles, and nucleus : all these, I say, are affected
by that very reproductive incapacity which is the character,
istic of the gametes, while they lack the potentiality of
karyogamic rejuvenescence possessed by the latter. In
the majority of Metazoa and Metaphytes the tissue-cells as a
rule suffer from the same impotence in virtue of their differ-