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jrIGi e.—The inner capsule of the same egg, seen from below (i.e., from the side directed towards the surface of attachment). Half the lower wall of the capsule has been removed by slitting along one of the lateral sutures, and along the median groove (mentioned in the text), to show the brown-colourec vitellus lying in the capsule. The continuity of the lateral sutures (I, s.) in front is well seen. The shaded area represents a depression which occurred in the wall of the inner capsule in the region of the area of attachment of the outer capsule.
the lower surface of the vitellus in an egg w hich had been allowed to develop for tw enty-four hours after being first seen. The large quantity of yolk points to the occurrence of a long period of incubation.
Sometimes the capsules of the egg are malformed, and, on opening such an egg, the vitellus is found to he already ruptured.
From the fact th a t in New B ritain I obtained m ature males of 'Nautilus pompilius, carrying a spermatophore in th e cephalic region throughout the year, I came to the conclusion th a t the reproduction of N autilus took place all the year round. I t now seems probable th at the breeding of N autilus, as of so many other forms, is subject to a definite law of periodicity.
Finally, it may be mentioned th a t N. varies with regard to the position of th e spadix on th e rig h t or left side, and also as to the origin of the siphuncular artery, in the same way as N. pompilius does. The male of N. carries a sperm atophore in the same position as in N. pompilius ; and, in fact, the only essential difference between the two species th at I know of at present, is the difference between the shells in the umbilical region.
