In brief, the evidence consists in showing that in the parasite a yolk-substance appears, which Smith says comes from the blood of the crab that produces it under the influence of the parasite. Incidentally, as it were, this is said to be the same yolk-substance (but no sufficient evidence that it is the same is given) that the egg stores up inside itself, and it is _assumed_ that it is a formative substance that causes the cell that gets it (or contains it or secretes it--details are wanting) to become an egg-cell. It is the excess of this substance produced by the male crab, while still a male, under the influence of the parasite, that affects the abdomen and its appendages in such a way that they assume the female condition. There are too many assumptions in the argument, some of which are scarcely of a kind that our knowledge of development, incomplete as it is, can allow us to accept without more direct evidence in their support, to make this view very plausible. Until better evidence is forthcoming, I fail to be convinced by Smith’s interpretation of his facts. Into Smith’s and Robson’s interesting observations on the blood of crabs, described in Smith’s later paper (part 7, 1911), it is not necessary to enter here, since the evidence taken as a whole offers little further in support of his view than had been already assumed. The argument on page 263 should not, however, pass unchallenged. Smith says: “It is clear that the old and familiar idea of an internal secretion produced by the gonad being the stimulus for the development of the secondary sexual character could not be applied here, since at the time that the alterations in the secondary sexual characters take place no ovary is present to give rise to the required stimulus. It is suggested, therefore, that in some way the stimulus must reside in the roots of the _Sacculina_,” etc. The argument seems to imply that, since the secondary sexual characters of the female can not be produced by an ovary in the infected male, therefore the _Sacculina_ must take the place of the ovary. But why make such a supposition, for if the testes simply keep down the development of the female characters, as Giard supposes, there is no need either for an ovary or for a _Sacculina_ to develop them. One might as well argue that since the cock does not develop the secondary sexual characters of the hen that an ovary is essential for their development--which is true, but not in the sense implied. Stamati (1888) states that he attempted to remove the testes of adult crayfish and apparently succeeded, but since no effects are expected until after a molt occurs (that may not take place for two years or more), no results were obtained. Injections of the gonads with an acid failed, since the animals died. E. EVIDENCE FROM INSECTS.