To sum up the evidence on the sex of the parasites, I was not able to discover a vestige of ova or ovaria in the two male Iblas; and I can venture to affirm positively, that the parasites of _S. Peronii_ and _S. villosum_ are not female. On the other hand, in the two male Iblas, I was enabled to demonstrate all the male organs, and I most distinctly saw spermatozoa. In the parasitic complemental male of _S. vulgare_, I also most plainly saw spermatozoa. In the parasites of _S. rostratum_, _S. Peronii_, and _S. villosum_, the external male organs were present. I may here just allude to the facts given in detail under Ibla, showing that it was hardly possible that I could be mistaken regarding the exclusively female sex of the ordinary form of _I. Cumingii_, seeing how immediately I perceived all the male organs in the hermaphrodite _I. quadrivalvis_; and as the parasite contained spermatozoa and no ova, the only possible way to escape from the conclusion that it was the male and _I. Cumingii_ the female of the same species, was to invent two hypothetical creatures, of opposite sexes to the Ibla and its parasite, and which, though Cirripedes, would have to be locomotive! I insisted upon this alternative, because if the parasite of _I. Cumingii_ be the male of that species, then unquestionably we have in _I. quadrivalvis_ a male, complemental to an hermaphrodite,--a conclusion, as we have seen, hardly to be avoided in the genus Scalpellum, even if we trust exclusively to the facts therein exhibited.