the point where the preparatory furrow sweeps round and enters. I believe that the cavity is lined by membrane, and that between the cavity and the body of the female, there is a complex membranous layer,--a pouch or bag being thus formed. An imaginary section of this pouch (with the thickness of all the parts extremely exaggerated and in a reversed position) is given in Pl. VI, fig. 1 _d´_: _a_ is the shell; _x_ the cavity, converted, as I believe, into a pouch by, firstly, the delicate tunic (_c_) lining the sack of the female; secondly, a double layer (_d_) of corium; and, thirdly, by a special, rather thick membranous layer (_b_), which thinning out round the cavity coats only part of the under surface of the scutum. This latter membrane I have not seen in any other Cirripede, and I believe it is nothing but the tissue, here not calcified, which, in a calcified condition, ordinarily forms the valves. On this view, the males may be said to be lodged in pouches, formed in the thickness of the valves. _Concluding Remarks._--The males from the absence of a mouth (and no doubt of a stomach), must necessarily be short-lived, and, I suppose, are periodically replaced by fresh males.[57] In one instance, the remnants of the two great compound eyes of the larva, could be seen at the end of the pouch, opposite the orifice. The larvæ, I conclude, crawl in at the orifice, one side of which is formed, as we have seen, of yielding membrane, and scratch out the dead exuviæ of the former occupant: certainly, the males are less firmly attached to their pouches, though some small quantity of cement is excreted, than are other Cirripedes to the objects to which they are attached. The small size of the female, and her valves not being thickly edged with chitine, accounts for the males having pouches specially formed for them, instead of being, as in _S. vulgare_, laterally imbedded in the chitine-border of the scuta. In hereafter weighing the evidence on the nature of the parasites in Ibla and in Scalpellum, the fact of the valves of the supposed female being here modified for the special purpose of lodging the males, will be seen to be important. If we imagine the male parasites to be extraneous animals, and that by adhering to the sack of the Scalpellum, they injure the corium and thus prevent the growth of the shell over an area exactly corresponding to their own size, and so form for themselves cavities; yet what can be said regarding the preparatory furrows? surely these narrow lines cannot have been produced by the pressure of the much broader parasites. Must we not see in the furrows, the first marking out, if such an expression may be used, of the habitation for the male, which has to be specially formed by the independent laws of growth of the female? [57] It is possible, though opposed to all analogy, that the females may be short-lived, and breed only once, in which case the males would not have to be periodically replaced.