The peduncle of the Lepads was formerly regarded merely as an organ of support, and even Cuvier discovered within it nothing but what appeared to him to be a homogeneous pulp, surrounded by muscular tissue. But, at certain seasons of the year, at least, there are, very distinctly developed, throughout the greater part of the soft matter which constitutes the bulk of the organ contained within the dense cartilaginous and muscular tunics, certain oval granules, regular, and uniform in shape, and gradually increasing in size. Poli and Lamarck were olopinion that these were truly eggs, but held that they were originally formed in the granular organ surrounding the intestine, (now regarded as the testicle,) and merely deposited here temporarily. But the recent researches of Professor Wagner and M. St. Ange have ren dered it probable that it is the ovary which is contained within the peduncle. The organ in question seems to occupy the whole of the pe duncle within the layers of muscular tissue. It is separated from the visceral cavity by a fine membrane which lines that cavity, and is a reflexion of the mantle. A transverse section of the ovary shews the eggs most fully deve loped towards the outer margin, and scarcely formed in the centre. There are also seen in the same section two canals which run longitu dinally through the organ, one near that side of the margin which corresponds to the anterior aspect of the body of the animal, the other in a similar situation on the dorsal aspect. Of these canals, the anterior is the larger ; and it alone was described by Cuvier, who regarded it as connected with the circulating system. The other was first described by M. St. Ange, who satisfied himself that it is a true oviduct. In Anatifa, he traced it pursuing a straight course through the ovary, and leaving it as a perfect canal just at the posterior and inferior angle of the organ, thence passing on the outer surface of the lining of the visceral cavity, in the groove of the dorsal valve, and terminating in an orifice opening into the visceral cavity not far from the brachial slit.* We have found a structure exactly resembling the above in Otion, where, however, instead of opening into the general cavity of the visceral sac, the duct is bifurcated just between the two auriform appendages, into each of which one of the branches of the duct enters and opens. M. St. Ange found eggs in progress through this duct; and they are frequently found, arranged in groups or packets, two or three in number, within the cavity of the mantle. We have not yet seen them in the duct; but the whole structure of the parts in question seems to indicate their adaptation to the function assigned to them by M. St. Ange. This being the case with regard to Anatifa, it appears to be very probable that the use of the singular auriform appendages in Otion is to afford a convenient lodging for the eggs before the young are hatcEed. Their deep sinuosities and folds seem to adapt them admirably ,to this purpose. Packets of eggs, however, are found within the cavity of the mantle in this species as in others. According to Burmeister, these packets are unattached, excepting in the earliest stage of development; but Wagner has generally found them fixed to a process of the mantle, situated near the adductor muscle of the shell which process is, at times, so much elongated as to admit of the eggs hanging out in groups from the brachial aperture, beyond the extremities of the arms. Burmeister has observed that, after the escape of the embryo, the shells remain connected with the parent, forming. a loose net-work. This author seenis to regard these groups of eggs within the man tle, and the tissue in which they are imbedded, as constituting the true ovary. In each of the individuals of Anatifa striata which came under his observation, he computed that there were about 4000 eggs in the ovary. Mr. Thompson calls these groups of ova conceptacles ; and says that " each has a separate attachment at the sides of the animal to the septum, which divides the cavity occupied by the animal from that of the pedicle." The retention of their ova, grouped in separate packets on the surface of their bodies, after their expulsion from the ovary, constitutes another point of resemblance between the Cirripeds and Crustaceous animals.
With regard to the anterior canal within the ovary, little has yet been determined. We have particularly examined it in Otion, and find that, like its fellow of the dorsal aspect, it leaves the ovary at its inferior edge, whence it opens into a small cavity situated between the intervalvular ligament and the lining membrane of the visceral cavity. We have not succeeded
in discovering any orifice in the walls of this cavity, although, from the results of some of our experiments we think it probable that there exists a small one just above the brachial slit. If so, is it not likely that this is the passage in tended for conveying the fecundating liquor from the orifice of the tubular process connected with the male organs to the ovary ? When the body is exserted through the brachial slit, the point of the process can easily be brought into contact with the outer surface of the cavity above described.
The development of the egg and the young of the Cirripeds has recently become an object of interesting inquiry in consequence of the novel results announced by Mr. J. V. Thomp son in his " Zoological Researches," (1830, 4th Memoir.) This gentleman has published an account of observations made on what he believed to be the young of Balanids, from which he concludes that, on their first exclusion from the egg, they closely resemble some of the branchiopodous crustacea,—that they pos sess the power of free locomotion through the water by means of setiferous arms projecting from within a bivalve shell,—and that they have very obvious pedunculated eyes. Minute animals, bearing these characters, and having some resemblance to species of the genus Cypris, were placed by Mr. Thompson in a glassful of sea-water. Soon after, on looking for them, he could not find them in the water, but he found in their room several very young balanids, which, from the appearance they pre sented, he concluded to be really the same animals that he had originally placed in the water, changed by metamorphosis. Mr. Thom p son has not seen the change actually going on, but he has satisfied himself that what he re gards as the free-moving embryo fixes itself by a spot on its dorsal aspect between the two shells, which spot can be seen during its free state. When fixed, the base of adherence ap pears to be broad like that of an Actinia : from this it rises in a conical form, truncated. The flat sides of this cone are coated with six shelly plates, so arranged as to leave a large space in the middle uncovered. This space is closed by the old shells of the embryo state, which are made to move up and down as the opercule does in the adult animal, admitting of the egress and ingress of the arms at the animal's pleasure. Through this shell two large black spots like eyes can be distinguished. Mr. Thompson found in the young of the Balanids, six pairs of arms, cleft ; each arm with' two ar ticulations. The first casting of the shell, after the animal has fixed itself, is followed by an increase in the number of articulations in each arm ; and this number is further added to at every succeeding shell-casting. Even the old full-grown animals, according- to Mr. Thomp son, cast their shells.
yery recently Mr. Thompson has made a still more satisfactory series of observations on the development of some of the Lepads, of the genera Cineras, Otion, and Lepas. These he obtained from tbe bottoms of vessels in the harbour of Cork. They hatched eggs in large numbers, and afforded hirn the means of ascer taining, entirely to his own satisfaction, that, at its first exclusion from the egg, the Lepad, like the Balanid, is a natatory crab. He found a considerable difference between the larve of the two classes. The newly-discovered one of the Lepads he describes as " a tailed monocu lus, with three pairs of members, the most an terior of which are simple, the others bifid, having its back covered by an ample shield, terminating anteriorly in two extended horns, and posteriorly in a simple elongated spinous process." The general appearance of this larva is not unlike that of the Argulus armiger of La treille." Very recently Messrs. Audouin,t Wagner,t and Burmeister,§ have corroborated the state ments and supported the views of Mr. Thomp son. Professor Burmeister has detailed the results of his observations with great minute ness. It appears that they were made chiefly on individuals of Anatifa striata, procured in the North Atlantic Ocean, and preserved in spirits ; partly also on Lepas anserifera. (Linn.) The results of these observations have led Pro fessor B. to divide the development of the Cir ripeds into five stages or periods. Thefirst of these is the state of egg ; the second is that of free locomotion ; the third is that in which the young becomes encased in a shell, and fixes itself; in thefourth stage, the young gradually assumes the characters of the adult ; the ,fifth stage is that of perfect development.