such effects on the ovary first change a male into a female so long as it is present and then when the parasite has disappeared leave an influence behind of a kind that causes the ovary to develop--an organ which the parasite destroys when the parasite is present? Is it not more probable that only the secondary sexual organs were changed, without change in sex, the single case of eggs observed being caused in another way? This point can only be settled by direct experimentation either by removal of the testis, by injuring it, or by injection, grafting, or feeding experiments. The extent of the testis and its position make it impossible to remove it by an operation, as I have found after repeated attempts. It seemed easier to destroy it by radium. This I have tried to do, using very powerful tubes, treating the crab (fiddler crabs) for several hours. The crabs had had one claw removed--the enormously large one--and were kept until the next molt, that occurred from a week to six weeks later. In none of the cases was any change produced. The large claw of the male regenerated, of course, not full size after only one molt, but after several nearly full size and always with the peculiarities of the male crab. The abdomen and the appendages were not changed. Whether the significant cells of the testes, if there are such cells apart from the germ-cells, were destroyed, can not be told, for as yet the histological examination of the material has not been made. Until a successful operation has been done, I think we must hesitate to accept Smith’s argument, although based as it is on a series of interesting observations. His speculation is as follows: “The reason why _Sacculina_ causes the assumption of the adult female state in _Inachus_ is found in the facts: (1) that the roots of _Sacculina_ elaborate a yolk-substance from the blood of _Inachus_ of a similar nature to that which is elaborated in the ovaries of an adult _Inachus_; (2) that in order to elaborate this yolk-substance the roots take up from the blood of _Inachus_ the female sexual formation substance, which is the necessary material for forming the yolk; (3) that the female sexual formative substance being absorbed by the _Sacculina_ roots is regenerated in excess; (4) that the presence of the female formative substance continually circulating in large quantities in the body-fluids of the infected crabs causes the production of adult female secondary sexual characters, and, when the parasite dies, of yolk-containing eggs.”