CILIA. 



613 



of the water was not produced by contraction 

 and dilatation of the tissue of the sponge, 

 which he showed to be destitute of irritability. 

 Dutrochet had made observations on the same 

 subject, which were published subsequently* 

 to those of Dr. Grant, and not anteriorly as he 

 supposes; he perceived the constant direction 

 of the current, and ascribed the phenomenon to 

 endosmosis and exosmosis. 



3. Ciliary motion of the ova of Polypi and 

 Sponges. The ova or gemmules of several of 

 these zoophytes execute independent move- 

 ments, and produce currents in the surrounding 

 water. This singular fact was, it appears, 

 first noticed by Mr. Ellis in 1755,f in ex- 

 amining a species of Sertularia, the Campanu- 

 laria dichotoma ; but he described the ova or 

 embryos which he had seen in motion, as 

 young polypi, already somewhat advanced in 

 their formation. Cavolini,| in 1784 and 1785, 

 observed the same phenomenon in the ova of 

 the Gorgonia and Madrepore, and investigated 

 it more fully. lie saw the egg-shaped gem- 

 mules or ova, on quitting the parent, rise to 

 the surface, and swim with their large end for- 

 wards, in a horizontal direction, till they fixed 

 themselves on some spot where they were deve- 

 loped. Dr. Grant, in 1825, discovered 

 similar motions in the ova of the sponge, and 

 detected the moving cilia. The cilia covered 

 the whole surface of the ovum, except the pos- 

 terior tapering extremity, and in its motions 

 the large end of the ovum was always directed 

 forwards. When an ovum fixed itself, its cilia 

 still continued to play, by which a current 

 along its surface was kept up for some time. 

 Dr. Grant also investigated the movements of 

 the ova of the Campanularia, previously seen 

 by Ellis, and of the Plumularia falcata. The 

 ova of both these zoophytes are contained 

 within transparent capsules, two or more being 

 in each capsule, surrounded by a clear fluid. 

 Dr. Grant distinctly perceived cilia vibrating 

 on the surface of the ova, and causing, while 

 within the capsule, an eddying motion of the 

 surrounding fluid, but propelling the ova 

 through the water when extracted from their 

 capsule, as in the sponge. The ciliary motion 

 has also been found in the ova of fresh-water 

 polypi, having been discovered by Meyen|| in 

 those of the Alcyonella stagnorum, which is 

 probably the same with, or at least nearly 

 allied to the Bell-flower Polype. 



By means of the remarkable provision here de- 

 scribed, the ova of these fixed zoophytes are dis- 

 seminated, and conveyed to situations suitable 

 to become the abode of the future individuals. 

 The same provision undoubtedly serves also to 

 move the water along their surface for the pur- 

 pose of respiration. It exists, as will be after- 



* L'agent immediat dumouvement vital devoile, 

 1826, p. 179, and Annales des Sciences Naturelles, 

 1828, torn. xv. p. 205. 



t Hist. Nat. des Corallines, p. 116. 



J Memorie per servire alia storia de' Polypi 

 Marini, Nap. 1785, p. 8, p. 48 of German trans- 

 lation. 





<S Edin. New Phil. Journal, vol. i. p. 150. 



Isis, 1828, p. 1225, sqq. Isis, 1830, p. 186. 



wards shown, in the ova of many other ani- 

 mals. 



4. AcalephtK. Many species of Medusae are 

 furnished with cilia, or at least with moving 

 organs bearing a close resemblance to the cilia 

 of other animals, though in the Medusae they 

 present several peculiarities. The cilia are 

 found in all the Medusae belonging to the order 

 Ciliograda of Blainville, or Ctenophora of 

 Eschscholz, of which the genus Beroe is a 

 good example. Eschscholz* describes them as 

 small pectinated or comb-like organs, ranged 

 in longitudinal rows or stripes on the external 

 surface of the body, with their flat surfaces in 

 apposition. Each comb-like organ consists of 

 many small, flattened, pointed filaments, united 

 together by a common base, the points being 

 directed towards the posterior extremity of the 

 body. They are moved like fins, being slowly 

 raised and suddenly struck back, by which 

 means the body is carried through the water. 

 In the Beroe and others of similar form, the 

 cilia point towards the closed extremity of the 

 body, so that the opposite or open end is 

 carried forward. The animal seems to have 

 the power of moving more or fewer of these 

 organs as it may incline, by which means other 

 motions besides direct progression are per- 

 formed. The cilia, when separated from 

 the body with a piece of skin, continue to 

 move briskly for some time. A longitudinal 

 vessel runs under each row of cilia, com- 

 municating with the rest of the vascular 

 system, and containing a fluid, in which yel- 

 lowish particles are suspended. Eschscholz 

 regards these vessels as arteries, and considers 

 1 the cilia as respiratory as well as locomotive 

 organs. Dr. Grant, in describing the cilia of 

 the Beroe pileus,f represents the parallel fila- 

 ments of which the comb-like organs consist, 

 as united together by a membrane as far as 

 their points, like the rays in the fin of a fish. 



Schweigger compares the vessels which run 

 underneath the rows of cilia, to the canals com- 

 municating with the tubular feet of the Sea- 

 urchin arid Asterias ; and Dr. Grant seems 

 also inclined to ascribe the motion of the cilia, 

 whose filaments he conceives to be tubular, to 

 their being alternately filled and emptied of 

 fluid derived from the longitudinal vessel,, like 

 the tubular feet of the Echinodermata. This 

 view of their mode of action, however, is 

 scarcely reconcilable with the observed phe- 

 nomena, as will be afterwards shown in con- 

 sidering the structure of the cilia in general. 

 Audouin believed that in the Idya, a genus 

 nearly allied to the Beroe, the fluid of the 

 longitudinal vessel, which he supposes to be 

 water, is sent into the cilia; he therefore 

 regarded them as respiratory organs. If the 

 vessel under the cilia in this case, as in the 

 Beroe, communicate with the rest of the vas- 

 cular system, and its contained fluid be re- 

 garded as blood, then the cilia of the Idya, 

 which, according to Audouin, are permeated 

 by the fluid, would bear a certain analogy to 

 the gills of fishes. 



* System der Acalephen, p. 3. 

 t Zoological Trans, vol. i. p. 9. 



