CHROMOSOMES, HEREDITY AND SEX. 
505 
two similar sex-cliromosomes/’ the male one like those of 
the female and one smaller or absent. The facts of sex- 
limited inheritance make it probable that in some groups the 
converse arrangement should be found, and two cases of this 
have already been described, while the writer has a third at 
present under investigation. The first account of unequally 
paired chromosomes in the female was that of Baltzer in the 
sea-urchins Strougy locentrotus and Echinus (4), in 
which he describes a hook or horse-shoe-shaped element 
in half the eggs, replaced by a rod in the other half. 
Tennent ( 60 ), however, on similar evidence, concludes that 
in American species of Hipponoe and Toxopneustes it 
is the male in which there is an unpaired chromosome, and 
those who have had experience of detailed study of Echinoid 
chromosomes will regard the question as still open until 
further confirmation is forthcoming. 
Recently an unequally paired chromosome in the female 
has been described in Lepidoptera, an order in which the 
probability of its existence had been predicted on the ground 
that sex-limited transmission occurs in the female. Seiler ( 52 ) 
describes in the eggs of the mothPhragmatobia fuliginosa 
a large chromosome which in one equatorial plate of the 
polar mitoses divides into two and in the other remains 
single. It may divide in either the inner or the outer plate. 
Since there are 27 ordinary chromosomes, the mature egg- 
may contain either 28 or 29. All spermatocytes have 28. 
Since the equatorial plate of the first polar spindle has 28, 
there is no evidence to show whether the eggs which have the 
divided chromosome give rise to males or to females. Seiler 
inclines to the view that eggs with 29 give rise to females, 
but it is possible that both the large chromosomes of the male 
are really compound, and that only one is compound in the 
female. 
The present writer has now^ under investigation a some- 
what similar case in Abraxas grossulariata. In normal 
females of this species the oogonia have 56 chromosomes, but 
in a strain in which abnormal sex-ratios appear there are 55 
