592 
CxEOPEREY SMITH. 
instances in wliicli tlie removal of the gonad inhibits in 
greatly varying degrees the development of the secondary 
characters. 
In attempting, therefore, to frame a theory which shall 
give a satisfactory account of the undoubted correlation which 
exists in various degrees between the primary and secondary 
sexual characters, we must bear in mind the variability of 
this correlation, and even in certain cases its non-existence. 
Mr. J. T. Cunningham, in a recent interesting paper (14), has 
put forward a theory which appears to me to fail in this 
respect. According to his theory the development of the 
secondary sexual chai’acters is due to the action of an internal 
secretion produced by the gonad, principally at its maturity. 
There can be no doubt that this statement is partially true, 
but it does not cover all the facts. If it represented the 
whole truth theabseuceof a differentiated gonad should in all 
cases be accompanied by the entire absence of all secondary 
sexual characters usually connected with it, and this is certainly 
not the case. 
We will now examine in some detail a particular instance 
which appears to throw a more definite light on the subject 
than any that has hitherto been obtained. The discovery of 
the phenomenon of parasitic castration Avas made by the late 
Professor Giard, and it always seemed to me very surprising 
that no one had followed up his discovery, since it affords a 
very obvious and simple Avay of gaining an insight into the 
nature of sex, without the necessity of performing a delicate 
operation Avith the clumsy means at our disposal. For in this 
case, instead of performing the operation ourselves, Ave find 
that Nature employs for the purpose some of the loAver classes 
of creation, Avho, though not endowed with the great intelli- 
gence Avhich is sometimes reported to be characteristic of man- 
kind, yet accomplish a thing' Avhich is not only impossible at 
present for a man to do, but also A^ery difficult indeed to under- 
stand. The spider crab, Inachus mauritanicus,^ is very fre- 
* By an imfortAinate error in nonienclatnre I. man ri tan icus (Lucas) 
was called I. scorpio (Fabr.) throngliout my monograph. 
