612 



CILIA. 



tube (m, n) were slight vortices in the current, 

 and at o near the end of the tube it came over 

 from the opposite side. Two currents were 

 continually going on in the mouth and 

 the stomach, one always flowing down the 

 sides in the direction e, e, and the opposite 

 one in the axis. Neither the cause of these 

 currents nor their use has been ascertained. 



Such are the phenomena of the ciliary and 

 other apparently allied motions in the Marine 

 Polypi. 



Spallanzani seems to have first noticed 

 them; he observed the currents produced 

 by the Flustrae, but erroneously attributed 

 them to the agitation of the arms, the 

 cilia on which he had not perceived. Dr. 

 Fleming* described the current along the 

 tentacula in the Valkeria cuscuta (a genus 

 which he has separated from the Sertulariae, 

 among which it was previously included,) and 

 distinguished the cilia with their undulatory 

 motion. Dr. Grantf discovered the cilia on 

 the arms of the Flustrae and described their 

 undulatory motion, to which he ascribed the 

 motion iu the water. He also pointed out the 

 revolving motion of particles within the mouth, 

 stomach, and rectum, and conjectured that it 

 was owing to the action of internal cilia, 

 which conjecture I have been able to verify. 

 Dr. Grant also discovered the vibratory and 

 probably ciliary motion within the mouth of 

 the polype of the Pennatulae. LoeflingJ 

 first observed the agitation of granular matter 

 within the stem and branches of the Sertu- 

 lariae. Cavolini afterwards more correctly de- 

 scribed this as a current of fluid holding 

 granules in suspension, running first in one 

 direction and then in the other. Lastly, Mr. 

 Lister observed anew these internal currents 

 of the Sertulariae, described them more mi- 

 nutely, and showed that they extended into 

 the stomach of the polypes. Mr. Lister has 

 also described the phenomena in the Flustrae 

 previously observed by Dr. Grant. He dis- 

 covered the currents within the stem of the 

 Tubularia, which, as far as I know, had not 

 been previously noticed. 



c. Sponges. In the various species of 

 sponges, water, the element in which they 

 live and grow, passes in currents through 

 pores and canals in their substance, in a con- 

 tinuous manner, entering at one place and 

 issuing at another. This phenomenon has not 

 been directly traced to the agency of cilia ; it 

 comes nevertheless to be considered here, as 

 such an agency is highly probable, and at 

 least the motion of the water is not owing to 

 any contraction of the canals in which it flows, 

 but is obviously caused by some other kind of 

 impulsion communicated to it by the surface 

 along which it passes. 



In a common sponge we see a number of 

 pretty large orifices on the surface, each opening 

 on the summit of a conical eminence or pa- 

 pilla (Jig. 296, a). These openings are named 



* Mem. of Wern. Soc. fol. p. v. p. 488. 

 t On the Structure and Nature of Flustrae. Ed. 

 New Phil. Journal, vol. iii. 1827. 



t Schwedische Abhandlungen, 1752, p. 121. 



Fig. 296. 



Sponge. 



by Dr. Grant the " faecal orifices." Innume- 

 rable small pores occupy the rest of the surface, 

 and give to it its peculiar character. These 

 pores penetrate to a certain depth, and lead 

 into canals (6), which, uniting together and 

 gradually growing larger, terminate in wide 

 tubes, which open at the faecal orifices. The 

 pores, excretory canals, and faecal orifices thus 

 form continuous passages through the sponge. 

 In the fresh state they are lined throughout with 

 a smooth gelatinous coating. 



When a living sponge is examined atten- 

 tively in its native element, the water is per- 

 ceived entering at the pores and issuing from the 

 faecal orifices, its course being indicated by the 

 motion of any floating particles that may be 

 present. The issuing currents are stronger 

 than the entering, and are rendered con- 

 spicuous by excrementitious matters or some- 

 times ova, conveyed out at the faecal orifices. 



When sections of the sponge, including a 

 greater or less extent of the internal canals, 

 are placed in water, the fluid, according to 

 Dr. Grant's observations, is still evidently 

 moved along the internal surface of the portions 

 of canals, although their continuity with 

 the rest is destroyed. Dr. Grant could not 

 detect cilia either in these canals or the pores 

 which lead to them, but he discovered these 

 organs on the ova of the sponge, which there- 

 by execute remarkable spontaneous motions, 

 and he is inclined to attribute the currents in the 

 adult sponge also to cilia, which he conceives 

 may probably exist, though, from their small- 

 ness, he has not been able to perceive them. At 

 any rate he has shewn by most satisfactory 

 observations, that the current cannot be ascribed 

 to contractions in the canal, for in none of his 

 numerous experiments instituted for the pur- 

 pose, could he discover any sign of irritability, 

 at least any sign of contraction of the tissue 

 of the sponge on the application of stimuli. 



Naturalists even of the earliest times, whose 

 attention was directed to the phenomena exhi- 

 bited by the living sponge, have remarked that 

 water entered and passed out from its porous 

 substance, but the true course of the fluid 

 seems to have been unknown, it having been 

 erroneously supposed to enter and issue by the 

 same orifices. Dr. Grant,* to whose labours 

 we owe most of the correct information ob- 

 tained respecting the structure and functions of 

 the sponge, demonstrated that the current is 

 continuous, and flows always in one direction 

 as above described, and proved that the motion 



* Edin. Phil. Journal, vols. xiii. xiv. Edin. 

 New Phil. Journal, vols. i. and ii. 



