There is apparently a connection between the stage of development of the horns and the age of the animal, as the following statement by Yarrell[16] (1858) indicates: “The fallow-buck is at his best in his sixth, or at most in his seventh year; after which, though the carcass may increase, the horns become smaller, and irregularly going back annually through something like their former stages of increase, a very old buck has from the state of his horns been mistaken for a young one. In the osteological department of the Museum at Paris there was, and may be now, the skeleton of a female reindeer in which the horns were reduced to little more than a rudiment of the beam and the brow-antler; this animal was so old that the molar teeth were worn down to the edges of the alveolar cavities.” At first sight these results in the fallow deer appear to be only an age condition, but since in old age a reverse process sets in, it may appear more probable that the amount of secretion by the testes or other glands may be the conditioning agent. In the case of the reindeer one may hesitate to ascribe the change to the ovary without further evidence. In cattle the effects of castration as seen in oxen have been studied. There is little here that is useful for our present purpose. The horns are not inhibited and may even be larger than in the bull. The absence of horns in certain races of cattle is apparently a dominant character, but as the character is neither sex-limited nor sex-linked, the evidence has no further bearing on the present topic. The effect of removal of the ovary from female calves has been studied by Tandler and Keller. The height of the ovariotomized female is less than that of the cow. The same difference is found between bull and ox. Tandler and Keller call attention to the similarity of the head in male and female lacking the gonads. They conclude that the ovariotomized female does not come to resemble the male, but that removal of the gonad causes both sexes to converge to a common type. Castration is frequently performed in horses, dogs, and cats, but as the secondary sexual differences, aside from size and behavior, are not very well marked in these animals, the results need not be here considered.