Mr Ritchie on ascertaining the Sex of the Chick in Ovo. 265 
rature of Europe in remote ages ; but the Greek and Roman 
descriptions of the climate of south and of central Europe 
1700 years ago, are so strikingly different from our experience* 
that some cause, more powerful than the feeble efforts of hu- 
man industry, is required to explain the change which has 
taken place ; and the migration of the isothermal poles has been 
strongly insisted on by Dr Brewster, as the chief cause of our 
improved climate. Dr Traill maintains the same argument, 
and endeavours to shew, that the accumulations and disruptions 
of the Greenland ice, and the coldness of ancient Europe, would 
appear, as far as our imperfect knowledge of magnetism in past 
ages will permit, to have a remarkable connection with magne- 
tic phenomena. 
Art. V .-—Notice of a mode by which a conjecture may be formed. 
as to the Sex of the Chick in Ovo . By Mr David Ritchie. 
In physiology it is interesting to ascertain at what period the 
embryo assumes a sex, and by what means its sex may be dis- 
tinguished. In regard to viviparous animals, such inquiries are 
attended with much difficulty, as accurate dissection and minute 
microscopic observation are necessary. Such investigations, too, 
cannot be carried on without cruelty. Hence it is that physiolo- 
gists have so often and so carefully observed and described the 
embryo in oviparous animals, from its first appearance in the 
egg till its complete development. For here the embryo may be 
subjected to examination without injury to the parent, and there 
is such similarity in the mode of growth of animals in the one 
case and in the other, that any fact ascertained as to the chick 
in the egg has usually led to a similar discovery in regard to the 
foetus in utero. The appearances presented by the egg have 
been described by the most celebrated anatomists of our own 
and of other countries. I shall advert to the opinions which 
have been entertained by them as to the egg, only in so far as 
they relate to my present subject. 
Eggs of the same bird differ from each other in shape. It 
has been asserted that the longer eggs contain males, the shorter 
ones females. To determine this, experiments were lately made 
