616 CILIA. 



In the inside of the body the membranous we may so express it, connected by others 



stomach (g) occupies the middle part, and which run vertically and transversely on the 



from it a pair of lobed coeca (h,hj (and i, i, cut coeca and on the roof and sides of the cavity, 



short) pass into each ray. Within the rays also (see the arrows infg. B ;) on the vesicles of the 



we find inferiorly the rows of vesicles (k, k) feet the course of these cross currents is varied 



which form part of the feet (1,1), and the by the curved surfaces. As the lining membrane 



ovaries. All the rays communicate through of the cavity extends into the respiratory tubes, 



the middle part, and the whole inside is lined so currents exist within these likewise, as at t, 



by a transparent membrane (n, n), which, fig. C. This is proved by injecting turbid 



like a sort of peritoneum, covers the stomach fluid into the ray, when particles are seen 



and cceca, attaches each of the cceca by a me- moving within the tubes; and if a few of the 



sentery (o, o) to the roof of the ray, lines the tubes with a portion of the skin be cut off and 



fibrous paiietes of the body, and is probably placed under the microscope, the fluid which 



reflected over the vesicles of the feet and the will still be retained by some of them may be 



ovaries. Each mesentery encloses a space seen to be in motion, the floating particles 



(o, fig. B) between its sides, which opens into moving from the base to the point and back 



the general cavity at the root of the cceca. The again, as in the arms of the Actiniae, 



lining membrane passes into the perforated 3. The motion is very distinct on the inner 



pits (e), by which the tubes (c) communicate surface of the stomach and creca; the currents 



with the cavity, and sends prolongations through within the cceca follow the same direction as on 



the perforations into the tubes lining them to their external surface, that is, an advancing 



their points. The space (s, s, Jig. B) lined by current runs inferiorly from the root to the 



this membrane contains sea-water, which is point and a returning one superiorly ; and at 



generally described as entering and issuing by the sides currents run upwards, following the 



the respiratory tubes.* ridges or folds of the internal membrane which 



I find the ciliary motion in four situations, result from the lobulated structure of the 



namely, 1. on the external surface; 2. within coeca. 



the cavity of the body, or in the space (s) 4. The ciliary motion exists distinctly within 



between its parietes and the viscera ; 3. within the feet, though the cilia are very small; these 



the stomach and cceca; 4. within the feet, became visible on viewing the edge of a folded 



In all these situations moving cilia are visible portion with Wollaston's doublet of one-thirty- 



with the microscope on the respective surfaces; fifth of an inch focus. 



they are every where comparatively small, in The currents described, as far as I have been 



some parts excessively so. Though I have not able to perceive, preserve always the same 



traced them over the entire extent of each sur- determinate direction. Even when portions of 



face, I have no doubt they exist at every point the ciliated surface are detached, the motion 



where currents are produced. on them continues, and its direction is the 



1. On the external surface. The ciliary mo- same as before their separation. 



tion as indicated by the application of pow- As to the use of these motions, it is most 



dered charcoal, occurs over nearly its entire probably connected chiefly with respiration; 



extent, but with different degrees of intensity, and if such be the case, it would show that in 



The strongest currents pass along the outer this animal a great extent and variety of parts 



surface of the tubes from the base to the point, are concerned in that function. The ciliary 



as at c ; they are also pretty strong on the motion on the inner surface of the stomach and 



claw-like processes (b' ) and intermediate skin; cceca is probably subservient also to the process 



on the feet they are evident but less vigorous. of digestion. It is conceivable that by means 



2. Within the body the currents take place of this provision the dissolved or digested food 

 on the lining membrane and its reflections. A might be introduced into the coeca, and spread 

 longitudinal current runs along the roof, and over their internal surface, there to be duly 

 another along the floor of each ray, forwards mixed with secreted fluids ' and subjected to 

 or towards its point: (see the arrows infg. A.) the process of absorption ; the returning cur- 

 These advancing currents are confined to the rent serving to bring back the residue, or to 

 median line and its immediate vicinity; two convey secreted fluids into the stomach. Or, 

 retiring currents (Y, r,) run backwards (one on considered as subservient to respiration, the cili- 

 each side) at the place where the sides join the ary motion, in diffusing the digested food over 

 floor of the ray. Two longitudinal currents also the internal surface of the cceca, may at the 

 exist on each of the coeca, an advancing one same time expose it to the respiratory influence 

 (ti ) on the inferior surface, and a retiring one of the water on their outside. 



superiorly (A, h, fig. A) in the space (o,Jig. B) These phenomena in the Asterias seem not to 



inclosed within the mesentery, w 1 ich, as already have been previously noticed. Tiedemann,* it 



mentioned, opens into the general cavity. The is true, had observed an eddying motion of the 



longitudinal currents, except those within the water in the vicinity of the respiratory tubes 



mesentery, are, if for the sake of explanation while the animal was slowly distending or 



emptying itself, but he conceived it to be 



* Without denying this mode of entrance, 1 nothing more than the commotion necessarily 



may yet mention that though I have often seen produced by the passage of the water through 



the animal slowly distending itself with water, and fi v r r i i-..i j i . . u 



again partially emptying itsflf, 1 could never per- the tubes ' rhere Can be llttle doubt that the 

 ceive the fluid entering or issuing at the orifices 



described. * Anaf. der Rb'hren Holothurie, etc. p. 40. 



