After the most careful dissection of very many specimens, and their examination in many different methods (as by caustic potash, &c.), I can venture positively to assert that there is no vestige of a mouth, or masticatory organs, or stomach: I did not see any anus, but I will not affirm that such does not exist.

In the upper part of the animal, lying under the superficial muscles, and close beneath the upper line of their attachment, I found in all the specimens, an eye, of a pointed oval form, rather less than 11/12,000ths of an inch in diameter, formed of an outer capsule, lined with purple pigment-cells, and surrounding, as it appeared, a lens. The eye is not introduced in [fig. 9], for I could not see it, except by dissection, and therefore do not know its exact relative position.

Generative System.—The contents of the animal, between the sack containing the thorax and the outer integuments, and directly under the thorax, varied much in condition: in young and lately attached specimens the whole consisted of a pulpy mass with numerous oil-globules; in other specimens, apparently more mature, there were vast numbers of cells, sometimes cohering in sheets, about 3/10,000ths of an inch in diameter, and having darkish granular centres; these I believe to be the testes, for in a specimen presently to be mentioned, in which the vesicula seminalis was gorged with spermatozoa, I found adhering to its outside, a mass of cells of exactly the same diameter, but now empty and transparent instead of having brownish centres. Lastly, in several other specimens, at the very bottom of the sack-formed animal, there was a brownish, pear-shaped bag, of different sizes in different individuals, and occasionally broader even than the thorax. This bag contained either pulpy matter, or a great mass of spermatozoa. Before being disturbed, these spermatozoa lay parallel to each other in flocks, and they yielded to the needle in a peculiar manner, so that I found (having had experience with these bodies in living Cirripedia) I could almost tell before examination under the compound microscope, whether or not I should see spermatozoa. Many had distinct heads,[52] which were two or three times as broad as the filamentary bodies; the latter when placed between glass were the 1/20,000th of an inch in diameter. I compared these spermatozoa with others taken out of the vesiculæ seminales of the individual hermaphrodite S. vulgare, to which the parasite was attached, and could not perceive the slightest difference in them. The brownish pear-shaped bag, or vesicula seminalis, the coat of which seems fibrous, could sometimes be distinctly traced, sending a chord or prolongation far up the thorax: at the end of the abdominal lobe, no doubt there is an orifice; and this, I believe, I once distinguished. Owing to this chord, the bag often adheres to the thorax, when the latter is dissected out of the general integuments; in this condition, I twice clearly made out that it was single: in one other specimen, however, there appeared to be two small vesiculæ seminales. By using a condenser and very brilliant light, the outline of the vesicula seminalis could sometimes be distinguished before dissection, at the bottom of the sack-formed animal; and such was the case in the specimen drawn in [fig. 9.]

[52] I do not understand the development of the spermatozoa in Cirripedia: in a recent Chthamalus and Balanus, I found the greater number had a little filament in front of the head or nodular enlargement, which latter varied in size and in shape from globular to that of a spindle. The filament before the head, also, varied in proportional length; it did not project in exactly the same straight line with the hinder part, and some of the spermatozoa were entirely without this filament in front;—such is the case with the spermatozoa here described.

Although I have dissected, at least, thirty specimens, taken at different times of the year, and from different localities, and when many of the specimens were mature and ready for the impregnation of ova, as clearly shown by the presence of innumerable spermatozoa, I have never seen even a trace of an ovum or ovaria.

Antennæ and Attachment.—The prehensile antennæ ([Pl. V], [fig. 10]), are seated a little above the very base of the sack-like animal; and this might have been expected from the antennæ in the larva, being seated on the ventral surface, not at the very extremity of the head. By a very strong light, they can sometimes just be seen whilst the parasite is attached to the hermaphrodite (the scutum of the latter having been cleaned on the under side), and are thus represented in [fig. 9]. They are formed of thicker membrane than the general integument of the body: the second segment, or disc, is pointed and hoof-like; when seen in profile ([fig. 11]), the upper convex surface has a uniform slope with the upper surface of the basal segment; it is furnished with a single backward pointing spine, attached, I believe, on the under side, nearly opposite the articulation of the ultimate segment: at the apex, there are some excessively minute hairs or down. The ultimate segment projects rectangularly outwards as usual, and has on its inner side, rather beneath the middle, a conspicuous notch ([fig. 12]), which bears two or three long, non-plumose spines; on the summit there are three or four rather shorter spines. On the outside of the great basal segment there is a single spine curving backwards. The importance of the following measurements (in fractions of an inch) will hereafter be seen.

Length of whole organ, from end of disc to the further margin of the oblique basal articulation38-39/6000
Length of whole organ, to the inner margin of the oblique basal articulation1/6000
Breadth of basal segment, measured half-way between the basal and second articulations,—the limb being viewed from vertically above8/6000
Length of hoof-like disc, measured from the apex to the middle of the articulation with the basal segment9-10/6000
Breadth of ditto5/6000
Length of ultimate segment6/6000
Breadth of ———— ———— beneath the notch7/20000
Breadth of ———— ———— above the notch5/20000

I did not see the cement-ducts, which, perhaps, was owing to the corium extending from the inside of the whole animal some way into the antennæ, thus rendering them rather less transparent than in common Cirripedes. That the ducts and cement-glands exist, is certain, for the antennæ in every case were enveloped in a little irregular mass or capsule of the usual, brown, transparent, laminated cement. When several of these parasites were attached close together, the cement ran up between them.

I may here state, that I found on one Scalpellum, three males very lately attached, and not as yet imbedded in the chitine border; they were white, opaque, pulpy, and full of oily globules; the lower part was considerably more pointed, and extended further beyond the prehensile antennæ, than in the older and imbedded specimens. There were distinct remnants of two great reddish-brown eyes, showing that in this respect the larvæ of the male in their last stage of development, are characterised like the larvæ of other Lepadidæ. The male larva would, probably, be a little larger than the male itself; but yet compared with the larva in the earliest stage, there can have been unusually little increase of size during the several intermediate metamorphoses; I judge of this from the dimensions of the larva of the hermaphrodite in the first stage, namely, 9/400ths of an inch, exactly the size of some of the smaller males. In the allied genus Ibla, the increase is also less than is usual, namely, from 15/1000ths of an inch, the diameter of the ovum, to only 25/1000ths of an inch, the length of the boat-shaped larva, just before its final metamorphosis.

Habits and Concluding Remarks.—The males are imbedded in the spinose chitine border of the occludent margin of the scuta, exactly over an oblique fold or notch ([fig. 15 á a]), close by the umbo. This fold has no direct relation to the males, but being present is taken advantage of by them; for it occurs in the young hermaphrodite, before the attachment of the males, and in species of the genus in which the males are attached to other parts. It occurs, also, in fossil species of Pollicipes, and in these it seems caused by the upper inner part of the valve being rendered more and more prominent during growth: in the present species, I suspect, its origin is connected with the formation of a ridge bounding the outer side of the pit for the adductor scutorum muscle: we shall see in the next species, that this fold is of the highest importance in relation to the position of the Males. The transparent chitine border of the scuta is broad, and fills up the fold in the shell, so that the outline of the occludent margin is not affected by it: in the drawing ([fig. 9]) some of the inner layers of chitine (e e), which dipped into and filled up the fold, have been removed, that the lower part of the animal might be more plainly exhibited. The chitine bears numerous spines of various lengths, which must afford some protection to the males, rudely arranged in lines, parallel to the edge of the valve, indicating the successively-formed layers of chitine; each spine has a fine, tortuous tubulus connecting its base with the underlying corium. The extreme outer edge of the border is thin, forming a kind of lip, close beneath which the delicate tunic lining the sack is attached. During continued growth, the valve is added to in thickness, and so is the chitine border, and likewise in breadth. It appears that the larva of the male must attach itself on the under side of this border, on the edge of the tunic of the sack, and that by the action of the cement, the corium beneath is killed (as I believe always is the case with other parasitic Cirripedia), whereas on both sides, the chitine continues to be added to, so that the male, excepting the upper and always projecting portion, becomes imbedded at first laterally, and ultimately all round: I have seen specimens in several different stages of imbedment. Hence, in old specimens, with a thick and broad chitine border, it might and does come to pass that one male is imbedded (the valve being laid flat) directly beneath another.