78 MARCUS M. HARTOG. 
hetercecism) in effecting rejuvenescence, and often replacing 
karyogamy: it is suggested that the evil effects of the pro- 
longed association of cell and nucleus are due (a) to the 
nucleus responding less actively to the stimuli from the cyto- 
plasm ; (0) its consequently inadequate directive power ; (c) to 
the resulting bad performance of its work by the cytoplast ; 
(d) to the imperfect nutrition of the nucleus; (e) the failure 
of the cell as an organic whole. 
19. The process of nuclear reduction in progametal cells 
and gametes is, though general, neither uniform nor universal. 
Its occurrence in the pollen-mother-cells of Flowering Plants 
leads us to anticipate its occurrence in the mother-cells of 
broods of reproductive cells generally, sexual or asexual. 
Pending the settlement of this point, explanation is premature. 
20. Replacement theories of fertilisation are inadmissible, 
since all fail to account for one or more of the following facts: 
(a) Multiple isogamy. 
(6) The non-discrimination of the broods of exo-isogametes 
into two categories, of which the members of either would pair 
with those of the other category, but not of their own. 
(c) The absence of “ excretion phenomena” of any kind in 
so many cases of gametogeny. 
(d) The existence of true parthenogenesis of male as 
well as female gametes. 
(e) The formation of a male individual from the exclusively 
female oosphere of the Hive-bee. 
We have now finished our task; the theory (theses 1—17) 
and the hypothesis (18) set forth are based only on facts lying 
in the fields of biological observation and experiment; an 
undertaking which should be more profitable than castle- 
building in the shadowy dreamland of 4 priori speculation. 
Cork, March 3, 1891.1 
1 Section VI, A was written after the completion of the rest of the MS., 
and again modified during its passage through the press. Slight alterations 
and additions have been made at the same time in the rest of the study 
(July 30th, 1891). 
