Observations upon the acquirement of secondary sexual characters, indicating the formation of an internal secretion by the testicle.

The question taken up in the present communication may be concisely stated as follows :— The most prominent and obvious function of the testicle is the formation of the sperm. Under normal circumstances this is discharged; it constitutes, that is to say, an external secretion. In spermatogenesis the male attributes culminate. There is, however, another element in maleness, of a different kind, less essential, yet in many cases well pronounced, viz., the acquirement of certain external characters which distinguish the male from the female in many groups of living forms.