466 
GEOFFREY SMITH AND EDGAR SCHUSTER. 
processes in the body, which do not pursue their normal 
course in the absence of the testicular cells. This disturb- 
ance of the normal metabolic processes of the body, resulting 
in the failure of the metabolic organs of the body to give rise 
to their normal products in normal quantities, may have the 
result of inhibiting the further development of the secondary 
sexual characters. The development of these latter cha- 
racters may depend, therefore, not directly on the action of an 
internal secretion or liormoue derived from the gonad, but 
on the elaboration of other products in other organs of the 
body in their due proportion. These substances may be 
tentatively called “ sexual formative substances,” but we have 
no reason for supposing that they are entirely devoted to 
sexual or reproductive purposes, and that they take no part 
in the ordinary metabolic processes of the body. In the case 
of the female individual in birds and Crustacea, reason has 
been shown in preceding studies for associating the develop- 
ment of certain female secondary sexual characters with the 
elaboration and transportation of large quantities of fatty 
material. In the case of the male we do not know what the 
nature of the corresponding material may be, but it is an 
obvious suggestion that it is some substance capable of being 
worked up into chromatic or nucleo-proteid material, and 
giving rise to cellular proliferation, as opposed to the storing 
of reserve stuffs, such as fat. The exact mode in which the 
gonad conditions in certain cases the production of these 
formative substances in the required proportions is not 
known. The idea that the gonad acts upon the other organs 
of the body by means of an internal secretion which it gives 
to the blood is really based on the analogy of other organs of 
internal secretion, such as the thyroid, pancreas, etc., but we 
claim that there is no experimental basis for the idea, apart 
from analogy. The gonad may equally well exert its action 
by taking up some substance or substances from the blood, 
thus altering the composition of the blood, and perhaps stimu- 
lating the continued production of these substances in some 
other organ of the body. This explanation was the basal idea 
