SOME PROBLEMS OF REPRODUCTION, 59 
entiation, so that the indefinite reproductive capabilities of the 
cells of Mosses and Begonias, Celenterates and Flat-worms 
are usually cited as exceptions to the rule; though the in- 
definite, if not unlimited, capacity for fissile reproduction 
must have been primitively inherent in every cell. The limita- 
tion of this power in most Metazoa occurs at a very early 
stage if the brilliant results of Chabry' prove to have a general 
application; for he has shown that in Tunicates the destruction 
of a single blastomere may determine the absence of the 
organ it should produce. 
C. The Adaptation of Gametes to Different Fates. 
Our next subject for parallel is the arrest or degradation of 
certain gametes of a brood, or, if we please, the favouring of 
single gametes of a brood at the expense of others. This isa 
common phenomenon of the struggle for existence between 
members of a colony, whether cells, organs, zooids, or even 
individuals, especially those destined for reproduction. Thus, 
in the ascus of the Truffle four to six spores are formed en- 
dogenously, but usually only one matures. In the Hetero- 
sporous Filicinez sixty-four megaspores are formed (in 
sixteen tetrads) in each megasporange; but only one matures, 
the other sixty-three undergoing complete disorganisation. In 
Eleocharis and other Sedges the pollen mother-cell under- 
goes two unequal divisions, just like the Metazoan ovum, and 
produces a single fertile pollen grain and three abortive ones. 
The ovarian ovum of Hydra attains its full size by devouring 
all the others in the ovary, and in many Arthropods the fertile 
ova develop at the expense of others. In Ascaris megalo- 
cephala some of the ova and spermatogonia are sacrificed and 
abort in the germ-tubes (O. Hertwig). In Vertebrates also 
many of the primitive ova are degraded to mere food material. 
As for organs and individuals, in Gymnosperms several 
archegonia may be formed and fertilised in each embryo-sac ; 
1«Embryologie Normale et Tératologique des Ascidiens Simples,” in 
‘Robin’s Journ. de |’ Anat.,’ 1887, p. 167, 
