Licence: Public Domain Mark
Credit: Cilia / by W. Sharpey. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![the right and descending on the left of each ovul, as viewed from without; but the cilia them- selves are very much, closer than the apparent teeth, and the illusion seems to be caused by a fanning motion given to them in regular and quick succession, which will produce the ap- pearance of waves, and each wave answers here to a tooth. Whatever little substances alive or inanimate the current of water brings, if not ejected as unsuitable, lodge somewhere on the surface of the branchial sac, along which each particle travels horizontally with a steady slow course to the front of the cavity, where it reaches a downward stream of similar materials (li) ; and they proceed together, receiving accessions from both sides, and enter at last, at the bottom, the oesophagus (h); this is a small flattened tube which carries them, without any effort of swallowing, towards the stomach. Mr. Lister observed similar phenomena in a species of Polyclinum, another form of com- pound Ascidia, in which an excretory funnel is common to several individuals. Mr. Lister, p. 385, has adverted to the resemblance be- tween the Ascidiae and a zoophyte of a similar form to that here described at page 7. I may here point out an analogy on the other side, no less striking, between the Ascidiae and bivalve Mollusca, in regard to the phenomena now under consideration. In both cases the water enters at one opening, and meeting with the surface of the membranous gills, passes through slits or interstices between their vessels into a space on the other side of the gill, which space terminates at another external opening, by which the water issues. In both cases also the mar- gins of the slits in the gills are fringed with cilia which exhibit a waving motion, the waves proceeding in opposite directions on the two borders of the slit. Lastly, in both cases, while the water and finer particles of matter floating in it pass through the slits, the coarser matters are conveyed along the first surface of the gills towards the mouth. The difference lies chiefly in the nature and form of the ex- ternal covering and the form of the gills in each; the membranous gills in the mussel being folded into double leaves on each side, and in the Ascidia being formed into a tubular sac; the space between the laminae of each leaf in the mussel corresponding with the space (f) enclosed between the branchial sac and mantle in the Ascidia, both these spaces leading to the excretory orifice. The remarkable appearances in the Mollusca described above could not wholly escape the notice of naturalists and microscopic observers. Thus we find Ant.de Heide,* a Dutch physician of the end of the seventeenth century, observing the appearance produced by the ciliary motion in the Sea-mussel; he names it motus radio- sus, or tremulus. He found it in most parts of the animal, but in none more evident than the gills (cirri pectinati), in which it is most easily examined. I call the motion radiant, says he, because it proceeds from the whole sur- • Anat. Mytuli, 8cc. l2mo. Atnst. 1684. face of the cirrus (gill) almost in the same way as air-bubbles issue from crabstones or metals while undergoing solution ; it may be called tremulous, because the parts affected by it vibrate. This motion goes on not only in the entire gill connected with the rest of the mussel, but even in the smallest pieces cut off' from it, which by their radiant motion swim briskly through the sea-water. Leeuwenhoek likewise appears, from various passages in his writings,* to have perceived the moving cilia in the Oyster and Mussel; he noticed also the existence of the motion in detached portions. His observations, so far as they go, are correct; but he takes no notice of the currents in the water; nor does he seem to have perceived the relation of the phenomenon to the respiratory or other functions, or indeed to have formed any opinion regarding its phy- siological use. Baker alludes to Leeuwenhoek's discoveries, and relates an appearance observed by himself in the l;resh-water Mussel, which must have been caused by the ciliary motion.f He states that on snipping off a piece of the transpa- rent membrane (gdl), and viewing it with the microscope, the blood will be seen passing through numbers of veins and arteries, and if the extremity of the membrane be viewed, the true circulation or the return of the blood from the arteries through the veins will be shewn. Dr. Hales, in his Statical Essays, (vol. ii. p. 93,) plainly alludes to the same phenomena. Among more recent writers, Professor Ehrman of Berlin, in a memoir on the blood of the Mollusca, published in the Transactions of the Royal Academy of Sciences of Berlin for 1816-17,]; has described an appearance. no- ticed by him in Mya, Anodonta, the Oyster, and other Bivalves, which seems evidently to have been produced by the ciliary motion. He states that on viewing the inner side of the labial appendages, accessory gills, or tentacula of these Mollusca, while it was illuminated by a strong light falling in a particular direction, he perceived a very rapid and incessant motion along the transverse stripes or furrows obser- vable on the surface of the part. The motion proceeded along each stripe like a series of oscillations. It continued for some time in portions cut off from the organ. He next ob- served that a number of round vesicular bodies escaped from the furrows or stripes at the part where they were cut, which bodies moved to and fro and as it were spontaneously in the water; and it seemed to him that in proportion as these bodies escaped, the oscillatory motion relaxed in intensity. From these facts he con- cluded that the motion apparent on the surface of the part was produced by the agitation of these vesicles or animated molecules within the furrows ; that is, he supposed the furrows to be covered by a membrane to which an • Epist. 83, in Opp. i. p. 463, 482. Anat. ct Contcmp. p. 52 in Opp. ii. Ibid. p. 27. Contiu. Arcan. p. 17 in Opp. ii. t Of Microscopes, &c. vol. i p. 128. t P. 214, sen.](https://iiif.wellcomecollection.org/image/b22282580_0023.jp2/full/800%2C/0/default.jpg)
