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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![S small bodies floating in the water were moved in a circular manner, but even many very minute animalcules, though able to swim vigorously, when diey approached the larger animalcules, were whirled about for some time in a circular manner. In announcing his discovery of the wheel animal,* he describes its rotatory apparatus as two projecting discs set round with very slender elongated organs. Imagine, says he, two wheels set round with points of needles, and moved very swiftly round from west by the south to the east. He adds that he cannot comprehend how such motion takes place in a living body. Lastly, in describing a small animal which he found adhering to the water-lentil, (probably a species of vorticella,) and speaking of the currents which it excites, and by which it attracts its food, he adds the following reflection :f More- over it is necessary that these animals, and in general all such as are fixed and cannot change their place, should be provided with an appa- ratus for stirring up motion in the water, by which motion they obtain any matters that float in the water, for their nourishment and growth and for covering their bodies. Baker,! next to Leeuwenhoek, takes notice of the cilia of animalcules. He observed them in many species, and named them fins, or feet, and sometimes fibrillae. He distinctly recog- nised the currents produced by them, and in- ferred the existence of cilia as the cause of visible currents in cases where the cilia them- selves could not be seen.§ In particular, he bestowed much pains in investigating the eco- nomy of the wheel animal previously disco- vered by Leeuwenhoek, and addressed a letter to the Royal Society on the subject, in 1744.|| He there describes its rotatory apparatus as a couple of semicircular instruments round the edges of which many little fibrillar move themselves very briskly, sometimes with a kind of rotation, and sometimes in a trembling or vibrating manner,^ by this means a cur- rent of water is brought from a great distance to the very mouth of the creature, which thereby is supplied with many little animalcules and va- rious particles of matter.** He also states that the wheels are instruments of locomotion by which the creature swims.ff Baker drew a distinc- tion between the rotatory and vibratory motions of the cilia, these organs being moved in some animals in the one way, in some in the other, while in others they seemed capable of being used in both ways.Jj; It appears that he was aware of the true structure of the so-called wheels, and though he often speaks of their * Continuatio Arcanorum Nature, 1719, p. 386, Epist. 144. t Epistolae Physiologies, 1719, p. 66. Epist. 7. t 1 cite his work entitled Of Microscopes, and the Discoveries made thereby, London, 1705, although his observations were previously related in separate memoirs of a much earlier date. j Of Microscopes, vol. i. p. 71, p. 80. ft Reprinted in op. cit. ii. p. 267. fl I'. 271. •* P. 2T.i. tt P. 284. U P. 292. being turned round, be was still doubtful of the reality of the apparent rotation. Spallauzani, in his curious and interesting researches on the production and economy of the Infusoria, made observations similar to those of Baker on the cilia and their motions. He describes them as small filaments or points agitated with a vibratory or oscillating motion. He conceived them to be organs of locomotion which the animals used in swimming,* and that they also served to excite a vortex or cur- rent by means of which food was brought to the mouth. The oscillating filaments cause the vortex; the vortex draws the floating par- ticles into the aperture or mouth of the animal- cule, and the latter chooses for its aliment the most delicate, or at least those which suit it best.f He afterwards describes the ciliary apparatus of die vorticella in a similar man- ner.]: In the account of his singular experi- ments on the apparent resuscitation of the Rotijer, he describes its wheel organs as two circles of filaments, exactly like the vibrating filaments of other Infusoria, which by their continued motion give rise to the appearance of two moving wheels; but he distinctly states that the rotation is only apparent, not real. These organs, he adds, serve the same purposes as the simple cilia.§ Needham,|| about the same time as Spallan- zani, correctly observed the cilia, and recog- nized their uses. SaussureU observed the cur- rents, but did not perceive the cilia. Pallas,** in his systematic work on Zoophytes, describes the eddies or currents produced by certain Roti- fera, and notices their cilia, but far less clearly than his predecessors. Wrisberg-|-|- observed the currents anded dies produced by the vorticellffi; at least he saw smaller Infusoria and particles of floating matter hurried on towards their mouths, but he seems not to have perceived the cilia. Otto Frederick Muller,JJ in his systematic work on the Infusoria, described the appear- ance and arrangement of the cilia in each species, and represented them in figures. He named them cilia and pili, and ascribed to their action the currents and vortices which the Infusoria excite. But while he assigns to them the office of locomotive organs, he denies that they are employed in seizing food; for, what is singular, in his long-continued and elaborate inquiries into the economy of these animals, he could never perceive that foreign matters drawn into the mouth were retained there as nourishment, but believed that they were always again thrown out. In this, however, he was undoubtedly mistaken. * Opuscules de Physique, torn. i. p. 180. t P. 183. t P. 199. j Tom. ii. p. 227. || Spallanzani, Nouvellcs Rccherchcs sur les Decouvertes Microscopiques, &c. 1769, p. 161. IT See Letter by Bonnet, in Spallanzani Opus- cules, torn. i. p. 176. *• Elenchus Zoophytoruni, 1766. tt Observationum de Aninialculis Infusoriis sa- tura, 1765, p. 52, p. 63. Vernniim Tcrrostriiim et Fluviatiliuni llis- toria, 1773, and Animalcula Infusoria, 1788.](https://iiif.wellcomecollection.org/image/b22282580_0007.jp2/full/800%2C/0/default.jpg)
