644 The American Naturalist. [August, 
the recent studies of Maupas upon the multiplication and con- 
jugation of the Infusoria, giving us a host of new ideas as to 
the cycle of life, the meaning of sex, and the origin of the 
sexual relation. 
In all this research and in the future outlook there are two 
main questions : 
1. What is the hereditary substance? What is the material 
basis of heredity, which spreads from the fertilized ovum’ to 
every cell in the body, conveying its ancestral characteristics ? 
Is there any substance corresponding to the hypothetical idio- 
plasm of Nägeli? 
2. What are its regulating and distributing forces? How is 
the hereditary substance divided and distributed? How far 
is it active or passive? l 
I may say at the outset that the idioplasm of Nägeli, a 
purely ideal element of protoplasm which he conceived of as 
permeating all the tissues of the body as the vehicle of hered- 
ity, has been apparently materialized in the chromatin or 
highly coloring materials in the centre of the nucleus. This 
rests upon the demonstration by Van Beneden and others that 
chromatin is found not only in all active cells, but is a con- 
spicuous element in both the ovum and spermatozoon during 
all the phenomena attending conjugation. 
Secondly, that while the chromatin is apparently passive, it 
is played upon by forces resident in the clear surrounding pro- 
toplasm of the nucleus, but chiefly by the extra nuclear archo- 
plasm, which seems to constitute the dynamic and mechanical 
factor in each cell. This, unlike the chromatin, only comes 
into view when there is unusual activity, as during cell-divis- 
ion, and is not evident (with our present histological tech- 
nique, at least), when the cell is arrested by reagents in any 
of the ordinary stages of metabolism. 
The Distribution of Hereditary Substance.—I may first 
review some of the well-known phenomena attending the dis- 
tribution of the chromatin substance to the tissues. 
I have borrowed from Parker figures by Carnoy to illustrate 
the resting and active stages of the cell, and from Watase, a 
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