556 
Nachdruck verboten. 
The Determination of Sex in Animal Development. 
By J, Bragp, D2 ses 
University Lecturer iu Comparative Embryology, Edinburgh. 
The following is a brief abstract of the chief conclusions to be 
found in a memoir’) bearing the above title, to be published else- 
where by the writer. 
A research into the problem of the determination of sex was 
forced upon the author by certain finds, relating to the germ-cells of 
Raja batis. From enumerations of the primary germ-cells of R. batis 
it presently became evident, that the total always approximated to 
one or other of two numbers; it was derivable either from 256 or 
from 512. From evidences to be given elsewhere it was established, 
that the larger number of primary cerm-cells related ‘to the future 
female embryos, the smaller to potential males. It was found, that 
in the smooth skate there were during the egg-cleavage germinal discs 
of two sizes. 
The above facts, for which the evidences are either already given 
elsewhere, or to be presented in a subsequent memoir on the germ- 
cells, formed the starting point for a prolonged investigation of the 
phenomena associated with the determination of sex. 
Sex in its origin in the Metazoa would appear to have been boul 
up with the constant differentiation of gametes of four categories. 
These were such, that two of them, the female- and the male-eggs, 
were formed within a sterilised Metazoan person, the female, while 
the development of the remaining two, the two kinds of spermatozoa, 
was alloted to a similar, but not identical, person, the male. The 
gametes of the female, that is, the two forms of eggs, possessed funct- 
ions different from those of the two kinds of spermatozoa of the male, 
and for this reason alone a sexual difference between the male and 
the female was bound to follow. 
Of the twofold gametes of the male it is to all appearance rare 
at the present time to find the full and complete differentiation of 
both in any given case, but this is known to happen in Paludina vivi- 
para (VON SIEBOLD, M. von Brunn, F. Mrves), Pygaera bucephala 
1) Read before the Royal Society, Edinburgh, on July Ist, 1901. 
