io6o The American Naturalist. 
there be one sex or two, and the presence of the latter merely 
complicates the question and nothing more. And all characters 
small or great, whether " sports " or other, have had a definite 
physical cause. 
The basis of the theory that acquired characters are not 
inherited is as follows : It is asserted by Weismann that the 
reproductive cells are separated from the primitive layers of the 
blastoderm at a very early period, and are set apart from those 
which develop into the other tissues and organs, so as to be unin- 
fluenced by all the later changes undergone by them. In the fe- 
male they develop into the ovarian cells, and in the male into 
the mother cells of the spcrmatozooids. It is claimed that this 
isolation is such as to protect them from influences which affect 
organs and tissues which compose the rest of the body, so that 
changes which arise in the latter are not transmitted to the former. 
Although we may see in the facts adduced by Weismann reasons 
for the conservatism of type possessed by the reproductive cells, 
there are various other facts, both of embryology and histology, 
which restrain us from attaching to the former the importance 
that the members of his school are accustomed to do. In the 
first place, since the reproductive cells are derived from the seg- 
mentation of the fertilized ovum, they partake of all the charac- 
ters, whatever they may be, which both parents contribute to the 
latter, in common with all of the other cells so derived. Now, 
since the other or *' somatic " cells develop the modifications 
which constitute evolution in their subsequent growth into or- 
gans, there is no reason why the reproductive cells which expe- 
rienced similar influences should not develop similar characters, 
so soon as they also are prepared to grow into organs. That 
such influences are experienced by the germ cells is rendered the 
more probable by the fact that their apjoearance after segmentation 
is often not immediate. In some of the rodent mammalia they 
do not appear until the thirteenth day after the first appearance 
of the blastoderm. Furthermore the isolation of these cells is 
not complete after the)- appear. The continuity of the reticular 
structure (cytoplasm) of the cells has been repeatedly demonstrated, 
an arrangement which is essentially connected with their nutrition. 
