512 
L. DONCASTEK. 
limited transmission by the male is only known in gi-oups 
(Diptera^ mammals) in which unpaired or unequally paired 
chromosomes have beeu found in the male, while of the two 
groups (Lepidoptera, Birds) in which sex-limited transmission 
by the female occurs, in one (Lepidoptera) two cases have 
now been described of an odd element in the female. It can 
hardly be coincidence that the spermatozoa should be dimor- 
phic in respect of a chromosome in the forms in which sex- 
limited transmission by the male takes place, and the eggs 
diamorphic in the same way in those in which sex-limited 
transmission is by the female. It should be noted also that 
the unpaired chromosome has been described as compound in 
tnammals, and one of the unequal elements as compound in 
Phragmatobia (moth) and possibly so in Drosophila, so 
supporting the suggestion that sex-limited inheritance is 
related to the association of a chromosome with the sex- 
chromosome. 
One anomalons observation, however, must be mentioned. 
Grnyer (24, 24a) has described an unpaired accessory chromo- 
some in the male of the fowl and guinea-fowl, although only 
sex-limited transmission by the female is known in birds (fowl, 
canary, pigeon). Either his observation is mistaken,^ or the 
facts are less simple than other cases would suggest. On 
WilsoiPs earlier hypothesis that both sexes are heterozygous 
for sex-factors, with selective fertilisation, the case causes 
no difficulty, although it is fatal, if substantiated, to the later 
hypothesis of the presence or absence of one single sex-factor. 
In this connection it may be mentioned that thei*e are some 
isolated instances which suggest that in cases which have 
normal sex-limited transmission by one sex, there may be 
partial coupling of the same characters with a sex-factor in 
the other sex. Such cases are so doubtful and irregnlar in 
their appearance that they cannot be regarded as evidential at 
present, but if they should be found to be genuine, they would 
also support the hypothesis that both sexes are heterozygous. 
^ As this goes to press, it has been contradicted by A. M. Boring and 
R. Pearl (‘ Jonrn. Exj). Zool.,’ xiv, 1914, p. 53). 
