On Reproduction, Animal Life Cycles. 81 
determinant hypothesis; and that is, by concluding that generaliza- 
tion consists in the maintenance of a perfect excretion process. Cells 
that come to lack some part of their excretory power suffer a loss in 
some of their energies, and only those cells can continue to hold all 
hereditable energies that do not accumulate waste products. 
In fact we find a number of acts performed by the germ cells that 
can be regarded as haying excretory value and which are not found 
in body cells. Probably there are a variety of such processes, but 
only three will be mentioned here, - and another a little later. One 
may well be the persistence in the nuclei of the germ cells of the 
full chromatin mass. The chromatin is proven to be such an im- 
portant center of metabolism that loss of some portions of it from 
the nucleus cannot fail to impair some growth regulation by the 
latter, consequently probably lessen excretory activity. So far as 
we know only body cells suffer such loss of chromatin . 7 
A second, and perhaps the most important method the germ cells 
avail themselves of for avoiding intoxication is, as we have tried to 
show, their act of separation from the contaminated soma. And a 
third one is by the process of cleavage of the egg. Thus, the egg cell 
in providing for the nourishment of the embryo secretes the sub- 
stances know collectively as yolk, sometimes in enormous quantity, 
and devotes a long period to their elaboration. But secretion is 
antithetic to excretion, therefore many waste substances must have 
accumulated in the cytoplasm of the egg during this process. In 
cleaving, the egg divides so that most of its cytoplasm and contained 
waste substances come to form body cells, whereby the line of germ 
cells become freed of this secretion and its waste accompaniments. 
The process of cleavage also by reducing the mass of the egg cells 
increases their surface extent and so facilitates excretion. In such 
ways as these the germ cells keep themselves permanently young, 
while body cells have no similar cleansing means. 
The asexual reproduction of Metazoa is any form of generation 
other than by a single egg cell. The two kinds of it, budding and 
fission, may be compared respectively with budding and fission of 
the Protozoa. In Metazoa such generation is undoubtedly secondary 
and not primitive, for if is far less widespread than generation by 
egg cells and does not occur in . most Yertebrates, Molluscs, Nema- 
7 The germ cells lose half of the number of chromosomes during the process 
of chromosomal reduction, but they retain in full one of each pair (kind) of 
chromosomes. Much oxyehromation is lost from the nucleus in the prophase 
of the first maturation mitosis, as is well known particularly in the case'' of 
the maturation of the ovocyte and which occurs to lesser degree in that of 
the spermatocyte; but this loss is simply a discharge by the chromosomes of 
waste products formed during the growth period of the germinal cycle, and 
it is greater in the ovocytes because their growth period is longer. 
