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 mother- 
cells destined by multiple fission to give birth toa 
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 con- 
fine 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 Strasbirger 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 through- 
out 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 sper- 
matogonia), perfect flagellates equipped with eye-spot, con- 
tractile 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- 
