4 MARCUS M. HARTOG. 
of gametes by rapidly repeated divisions of a cell—the 
gametogonium ; 
(2) That the alleged nuclear excretions in the Metazoan egg 
and the Ciliate “ gamete,” &c., represent true gametes arrested 
in their development ; 
(3) That the so-called “ excretions” of protoplasm in plants 
are of various kinds, many of which are homologous neither 
with the former process nor with one another ; 
(4) That the use of the rapid preliminary divisions is a 
purely physiological one; that is, to induce by exhaustion 
the same reproductive incapacity that would otherwise 
require a long series of slowly repeated divisions. 
On these lines we can account for all the facts, from the 
simplest cases of the formation of isogametes to the most 
peculiar phenomena of oogeny and spermatogeny ; phenomena 
which the sexual replacement theories of Minot, Balfour, and 
van Beneden, on the one hand, and the more complex replace- 
ment theory of Weismann, on the other, only profess to 
explain in the higher groups. The views here put forward 
are essentially a development and extension of what we may 
term the “ morphological theory” of polar bodies, first enun- 
ciated by Giard, Biitschli, Whitman, and Mark,! and advocated 
especially by the Hertwigs. It will not seem strange that 
this view has never had full justice done it when we reflect 
that it is to men who have worked especially at the Metazoa 
that we owe the greatest debt for shaping our biological 
theories; and that our gratitude has, perhaps, led us to be 
too unquestioning in our attitude of discipleship to such re- 
spected masters as Balfour, van Beneden, and Weismann.’ 
The exposition of the processes of gametogeny naturally leads 
1 Mark was the first definitely to express the view that the polar bodies 
represent abortive ova; see “ Maturation, Fecundation, and Segmentation of 
Limax campestris,” in ‘Bull. Mus. Comp. Zool. Harv. Coll.,’ vol. vi, 1881. 
* I may say that I never doubted that some replacement theory of 
fertilisation was sufficient to cover the facts, till I read and meditated over 
Maupas’s account of the conjugation of the Ciliata; and this it was that first 
weakened?my belief, not only in replacement theories, but also in the “ pre- 
liminary excretion” theory on which the others were founded. 
