Cirrhopoda / [John Coldstream].

John Coldstream

Date:: [1837?]

Credit: Cirrhopoda / [John Coldstream]. Source: Wellcome Collection.

11/16 page 11

$gradually increasing in size. Poli and Lamarck were of opinion 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 animat, 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 hatched. 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 * Professor Wagner says, “ at the base of the dorsal valve there exists a slit in the mantle which leads into the canal that runs through the peduncle. I presume that this canal serves as an oviduct, and that the slit is analogous to the opening of the I branchial canal in the bivalves/’ (in Archiv fur \ Anat. Physiol. &c. von D. J. Muller, 1834, No. 5, l quoted in Ann. des Sc. Nat. iv. n. s.) We are not \ aware what species was anatomized by Professor 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 seems 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 tuey pre¬ sented, he concluded to be really the same animals that he had originally placed in the * Phil. Trans. 1835, 356.$

Cirrhopoda / [John Coldstream].

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