The Facts of Sex in Relation to Metabolisin. 249 
XXI. The Facts of Sex in Relation to Metabolism: A Review 
of some recent Theorves. By J. AnTHUR THOMSON and 
NorMAN WYLD. 
(Read 20th April 1892. ) 
1. OBJECT OF THE PAPER.—The students of nature range 
themselves into two parties distinguished by their practice. 
There are some who, whether from carelessness of the results 
to be gained, or from respect for the complexity of otherwise 
tempting problems, refrain from the theoretical interpretation 
of facts, and keep themselves to the collection and arrange- 
ment of experiences ; and there are others who, undeterred 
by failures, venture hypothesis after hypothesis until one 
that fits is found. The history of science is the justification 
of both. The present paper neither brings new facts nor 
offers new solutions, but is an estimate and co-ordination of 
some recent suggestions as to the significance of sex. 
2. HistoricAL Nore.—Although some knowledve of the 
facts of sexual reproduction dates from ancient times, no 
precise analysis of any one of the problems involved was 
attempted, nor could have been attempted with success, 
until after embryology had begun to rise on a sure founda- 
tion. When we remember that it was only in 1843 that 
Martin Barry—a student of whom Edinburgh is proud— 
observed the union of spermatozoon and ovum, we under- 
stand how recent all scientific theories of sexual reproduction 
must be. It is true that Blumenbach in the last century 
spoke of four hundred theories of sex, and himself ventured 
a four hundred and first, but these were for the most part 
confined to speculative suggestions as to what determines 
whether an embryo will become a male or a female—they 
were not general theories of sexual reproduction. From 
various positions, since embryology ceased to be infantile, 
important steps were made, notably Darwin’s theory of 
Sexual Selection. But even when we take account of all 
the suggestions offered, eg., by Owen, Leuckart, Minot, 
Brooks, Rolph, Simon, Sabatier, Hertwig, and Weismann, 
and of Hensen’s valuable monograph contained in Hermann’s 
Physiologie, we must, as it seems to us, admit that the first 
