CILIA. 



617 



phenomenon he saw was caused by the ciliary 

 motion on the external surface, though he was 

 not aware of this. 



Having entered into these details respecting 

 the Asterias, I may describe more briefly the 

 phenomena in the Sea-urchin, the more so as 

 my opportunities of observing this animal have 

 been less frequent. 



The species submitted to examination was 

 the common large Sea-urchin of our shores, 

 Echinus esculentus, described by Monro.* 

 Its body consists of a globular shell, containing 

 the viscera. The mouth is placed underneath, 

 the anus opposite on the upper surface. The 

 tubular feet are disposed in vertical rows from 

 the mouth to the anus, the intermediate part of 

 the shell being covered with moveable spines, 

 and the singular claw-like organs referred to in 

 describing the Asterias. As in the Asterias, 

 there are membranous respiratory tubes, but 

 they are comparatively few in number, forming 

 ten small bunches or groups, which are placed on 

 the under surface not far from the mouth, and 

 open internally in ten small perforated pits, like 

 those of the Asterias; they are supposed by 

 Tiedemann and others to be the channels by 

 which the sea-water gets into the interior of the 

 body, and fills the space between the inside of 

 the shell and the contained viscera. The ali- 

 mentary canal, commencing at the mouth, rises 

 through the curious dental apparatus named 

 Aristotle's lantern, turns in a waving manner 

 twice round the inside of the shell, and termi- 

 nates above at the anus ; it is supported by a 

 mesentery derived from a membrane which lines 

 the cavity of the shell, and which is reflected 

 over its contents like a peritoneum. Inside the 

 shell we also find the ovaries and the rows of 

 feet. The internal parts of the latter, instead of 

 being round vesicles as in the Asterias, are broad 

 laminae enclosing vessels,f canals or branched 

 cavities, which canals, like the vesicles of the 

 Asterias, communicate on the one hand with 

 the tubes of the feet, and on the other with a 

 common vessel which runs along the middle of 

 each double row of laminae. The vessels or 

 spaces within the laminae are much branched ; 

 they form a plexus surrounded by a principal 

 vessel at the border. 



I have found the ciliary motion over nearly 

 the whole surface of the cavity of the body and 

 the contained parts, which surface, as mentioned 

 already, is covered by a lining membrane or 

 peritoneum. Two longitudinal currents run on 

 the intestine in the same direction, viz. one 

 along the line of attachment of the mesentery, 

 the other at the opposite part of the tube. On 

 the remaining circumference of the intestine 

 the impulsion is directed obliquely towards the 

 nearest longitudinal current. In regard to the 

 laminae of the feet, a current runs down the 

 middle of each of the double rows, following 

 the course of the longitudinal vessel there 

 situated, the direction being from the anus to- 

 wards the mouth. Lateral currents pass over 

 the surface of the laminae from their external 



* Anatomy of Fishfs, &c. 

 t Accurately described by Monro, 1. c. 

 VOL. I. 



to their internal border, where they join the 

 middle current; they follow the irregular eleva- 

 tions on the surface of the lamina? occasioned 

 by the canals or vessels in the latter; hence, 

 when charcoal powder is applied, the particles 

 follow winding paths in crossing from one edge 

 of the laminae to the other, and they are fre- 

 quently caught in a hollow between two cur- 

 rents, and whirled about for some time before 

 they resume their way. Currents were visible 

 also on the reflections of the lining membranes 

 which cover and pass between different parts of 

 the lantern, and at the internal openings of the 

 respiratory tubes. The cilia on the parts de- 

 scribed are excessively small, but distinctly per- 

 ceptible. The ciliary motion was not detected 

 on the external surface of the body nor within 

 the alimentary canal; but in regard to these 

 parts the observations could scarcely be consi- 

 dered as conclusive; nor could 1 determine whe- 

 ther, as in the Asterias, the phenomenon occurs 

 within the feet or within the spaces or vessels 

 of their membranous laminae, though from an 

 observation of Carus, who states that he saw 

 globules circulating within these laminae, its 

 existence in that situation is not improbable.* 



This provision in the Echinus is probably, as 

 in the analogous cases already described, chiefly 

 subservient to respiration. Tiedemann, who 

 ascribed a respiratory office to the water within 

 the animal, expresses himself at a loss to con- 

 ceive by what mechanism it can be made to 

 enter and issue from a cavity with unyielding 

 sides incapable of being expanded and con- 

 tracted by muscular action ; perhaps the provi- 

 sion here described may be adequate for this 

 purpose. Since the above observations were 

 made, a fact has been mentioned by Ehrenberg,f 

 from which it appears that the ciliary motion 

 exists on the external surface of the Echinus on 

 the spines. The species observed by him was 

 the Echinus sexatilis. The observations of Carus 

 and Ehrenberg here referred to comprehend 

 the only facts hitherto published on the ciliary 

 motions of the Echinus which have come 

 under my notice. 



7. Annelida. In proceeding to describe the 

 ciliary motion in animals of this class, in 

 several of which it occurs, it seems advisable 

 to begin with the Aphrodita, as the phenomena 

 in this animal present a remarkable analogy 

 with those we have been considering in the 

 Echinodermata. 



A great part of the body of the Aphrodita 

 aculcata, or Sea-mouse, (of which Jig. 299, A, 

 represents a cross section,) is occupied by the 

 abdominal cavity, (a, a, a.) Along the superior 

 wall of this cavity a row of cells (b) is placed 

 on each side, which below open into the abdo- 

 men, but above, or exteriorly, project on the 

 dorsal surface as oblong transverse eminences. 

 Each alternate cell on the back bears a broad 

 membranous scale (c, c), and each of the in- 

 termediate ones a small indented process. On 

 the back a covering of felt-like substance (d) 

 is stretched from side to side like a roof over 



* Analecten zur Natur-vrifwenschaft, etc. Dres- 

 den, 1829, p. 152. 



t Muller's Archiv. Band 1, p. 578. 



2 s 



