708 
discoveries of any great usefulness in the 
work of producing new and improved races 
of plants and animals, however useful it 
may have proved in other directions, or 
may yet be in genetics. 
Another method of study has been that 
of the cytologist. A long list of able in- 
vestigators have in recent years given at- 
tention to the phenomena of cell division, 
especially the process by which gametes, 
or reproductive cells, are produced. Very 
soon after the rediscovery of Mendel’s 
principles cytologists pointed out that the 
behavior of the chromosomes in the reduc- 
tion division is sufficient to account for 
Mendelian phenomena if a proper connec- 
tion between the chromosomes and Men- 
delian characters could be proved. One of 
the most important results achieved in this 
line of investigation is the demonstration 
of a relation between certain chromosomes 
and the determination of sex. The work 
of Professor E. B. Wilson has been espe- 
cially convincing in this respect, though 
many other investigators, especially Pro- 
fessor Morgan and Miss Stevens in this 
country, and Boveri, Baltzer and others in 
Europe, have contributed important re- 
sults. The net results of these investiga- 
tions are that in most species the female 
possesses a pair of chromosomes of peculiar 
character, usually distinguishable from the 
other chromosomes, and, because of their 
behavior in the prophases of the first matu- 
ration division, called by many cytologists 
“<jdiochromosomes.’’ The male has only 
one of this type of chromosome. From the 
behavior of these idiochromosomes it re- 
sults that all the eggs contain one idiochro- 
mosome, while the sperm is of two kinds, 
one containing a single idiochromosome, 
the other none. Eggs fertilized by the 
former produce females; by the latter, 
males. In a few species the female has 
only one of these peculiar chromosomes, 
SCIENCE 
[N.S. Vou. XXXV. No. 907 
while the male has none. In these species 
the female produces two kinds of eggs, 
one female-producing, the other male-pro- 
ducing; while the male produces only one 
kind of sperm. These investigations have 
thus given strong reasons for believing that 
sex is an inherited character, and is hence 
not determined by external conditions. 
These facts have been demonstrated for 
a large number of species (over a hun- 
dred), including man. 
While in most species the male possesses 
but one of these presumably sex-determin-. 
ing chromosomes, it frequently happens. 
that this chromosome has a synaptic mate, 
which, however, appears not to be con- 
cerned in sex production. This synaptic: 
mate consists in some eases of a single chro-- 
mosome; in others it consists of a group of 
chromosomes varying in number from 2 to 
5 in different species; in still others it is 
wanting entirely. These facts are of spe- 
cial interest in connection with the further 
fact that a large number of ordinary so-- 
matic characters have been found to form, 
Mendelian pairs with the sex element.. 
Thus, in barred Plymouth Rock poultry 
the barring of the feathers is transmitted! 
by the female only to her male offspring.. 
Many human affections are transmitted in. 
a similar manner, such as night blindness, , 
color blindness, ete. Pearl has shown that- 
high egg-laying quality in poultry is sim-. 
ilarly sex-limited. Females do not trans-. 
mit this quality to their daughters, but do. 
transmit to their sons the power of trans-- 
mitting to the granddaughters high egg-- 
laying quality. A long list of such sex-- 
limited characters has been demonstrated. . 
These facts raise the presumption that these - 
sex-limited characters are related to the- 
chromosomes—in what manner of course: 
we do not know. 
On the history of the chromosomes dur-- 
ing the life history of the cell, especially- 
