508 
L. DONCASTER. 
two of the chromosomes of the female are sex-chromosomes. 
The male, with half the number, has only one, but since all 
spermatozoa bear it, all fertilised eggs have two, and so 
become females. Similar suggestions had previously been 
made by Wilson and others. 
In this connection mention should be made of the conditions 
found in Rotifers, about which there has been some contro- 
versy, but the facts appear fairly clear. In Hydatina, 
Lenssen (30) has shown that in the parthenogenetic eggs 
which will become females one polar division is suppressed, 
while it takes place normally in male-producing eggs and in 
eggs which will be fertilised (‘^Dauereier^^). He believed that 
female-producing parthenogenetic eggs produced no polar 
body, male-producing eggs and Dauereier, one. Whitney 
(63), however, has shown that female-producing eggs have one 
polar body, male-producing eggs two. The present writer 
has confirmed Lenssen^s observations on the suppression of a 
polar division while the egg is in the oviduct,^ but all the 
observations can be brought into line by assuming that in 
female-producing eggs the first polar division is suppressed, 
but that the second takes place normally after the egg is laid, 
and that in male-producing eggs the first takes place before, 
the second after laying. In Rotifers, therefore, as in Hymen- 
optera, the female probably has the diploid, the male the 
haploid number of chromosomes. 
This completes the main lines of evidence connecting sex- 
determination with chromosome behaviour, apart from those 
derived from the facts of sex-limited transmission. 
(3) Sex-limited Inheeitance and Chromosomes. 
Sex-limited inheritance may be defined as the transmission 
by individuals of one sex of a factor only or almost exclu- 
sively to offspring of the other sex. In different groups it 
occurs in different sexes. In the first cases to be discovered 
(Abraxas, canary, fowl) the female transmits certain 
^ Unpublished. 
