In the second edition of Professor Owen's Lectures on the Invertebrata (1855), I find no mention of Valenciennes' discovery of the additional four apertures; but the author states that "on each side, at the roots of the anterior branchiae, there is a small mamillary eminence with a transverse slit, which conducts from the branchial cavity to one of the compartments of the pericardium containing two clusters of venous glands. There are also two similar, but smaller, slits, contiguous to one another, near the root of the posterior branchia on each side, which lead to and may admit sea-water into the compartments containing the posterior cluster of the venous follicles." In this work the ovary is not only described, but _figured_, on the right side of the gizzard. The figure, however, rightly places the greater part of the ovary below that organ. [Illustration: _Nautilus pompilius._ Fig. 2. Natural Size. The pallio-visceral ligament seen from below: torn on the right side to show the rectum and oviduct; cut through on the left side along the dotted line close to _d'_ in the preceding figure. _a._ Anus. _b._ Oviducal aperture. _c._ Heart. _d._ Left branchial veins. _e._ Right branchial veins. _f._ Oviduct cut through. _g._ Ovary. _h._ Rectum. _i._ Mantle. _k k k._ Pallio-visceral ligament; _k'._ its torn portion. The oval "aperture for the siphonal artery" is seen to the left of _c'_, and the right-hand style in _Fig._ 1 passes through it.] On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection. By CHARLES DARWIN, Esq., F.R.S., F.L.S., & F.G.S., and ALFRED WALLACE, Esq. Communicated by Sir CHARLES LYELL, F.R.S., F.L.S., and J. D. HOOKER, Esq., M.D., V.P.R.S., F.L.S., &c. [Read July 1st, 1858.] London, June 30th, 1858. MY DEAR SIR,--The accompanying papers, which we have the honour of communicating to the Linnean Society, and which all relate to the same subject, viz. the Laws which affect the Production of Varieties, Races, and Species, contain the results of the investigations of two indefatigable naturalists, Mr. Charles Darwin and Mr. Alfred Wallace. These gentlemen having, independently and unknown to one another, conceived the same very ingenious theory to account for the appearance and perpetuation of varieties and of specific forms on our planet, may both fairly claim the merit of being original thinkers in this important line of inquiry; but neither of them having published his views, though Mr. Darwin has for many years past been repeatedly urged by us to do so, and both authors having now unreservedly placed their papers in our hands, we think it would best promote the interests of science that a selection from them should be laid before the Linnean Society. Taken in the order of their dates, they consist of:--