516 
L. DOXCASTER. 
indicated the means by which it is affected in sacculinised 
crabs, and it is conceivable that other causes, such as 
staleness of the eggs before fertilisation, might from the 
beginning change the metabolism (perhaps by destroying the 
activity of a sex-chromosome,’^ as suggested by Pearl and 
Parshley (50) ), in such a way as to cause an originally female- 
producing egg to develop into a maled 
The general conclusion must be that although the observa- 
tions connecting a particular chromosome with the determina- 
tion of one sex are in many cases indisputable, there is no 
evidence to show how this chromosome acts; and that, since 
the sex of the offspring is in some cases modifiable by environ- 
ment, it is probable that the presence of the chromosome is 
associated with a particular kind of cell-metabolism, of which 
sex is to be regarded rather as a visible expression than 
as a cause. 
Summary. 
In the first section a summary is given of the main lines of 
argument leading to the conclusion that Mendelian charac- 
ters are determined by chromosomes.” Some indication is 
given of the restrictions which must be placed on the meaning 
of this phrase in respect of the part played by the cytoplasm in 
heredity. It is concluded that the arguments in its favour, 
though very strong indirectly, are not supported by sufficient 
direct evidence to be regarded by themselves as indisputable. 
In the second section the chief classes of facts are reviewed 
which suggest a relation between chromosomes and sex-deter- 
mination, and a preliminary account is given of a new case 
of an unpaired sex-chromosome” in the female, in a strain 
of the moth Abraxas. It is concluded that the arguments 
for a relation between chromosomes and sex are much 
^ The production of workers from female-iDrodncing eggs of the 
Hymenoptera is possibly a comparable instance. A change of meta- 
bolism induces fundamental differences in structure between individuals 
whose inherited constitution is identical, and these differences are of 
essentially the same nature as those which distinguish the two sexes. 
