471 



F.CHIVODERMATA. 



ECHINODKRMATA. 



motions are ilow, but in Opkioeoma they are comparatively 

 rapid, and manifested in actire contortions on some occasions. 

 According to M. Sara, the young of Atteriai nffinolento, which 

 bar* four abort dub-abapd appendages or arms at their anterior 

 extremity, more slowly but uniformly in a itraight line with their 

 fora arm* foremost Vibratile cilia are supposed to form the moving 

 power in thi* caw : the arms alao enable the little animal to creep 

 at a alow pace along the rocks. When the animal is more fully 

 developed the power of swimming ceases. 



Tiedemann consider* that the power of moving the rays resides in 

 the contractile skin. Mockel states that there are distinct muscles 

 leading between the calcareous plates which form the floor of the 

 rays. Dr. Sharpey has no doubt that the motions are partly effected 

 by the skin, but he had himself observed a distinct band of muscular 

 fibres running along the roof of each ray, between the coriaceous skin 

 and peritoneal membrane when it U stripped off. 



Bat the principal looemotive organs of the EMnodermota are the 

 membranous tubes which can be protruded at will through the 

 ambulacra! apertures, and which have been termed the feet The 

 clearest description of this complicated and in some degree obscure 

 apparatus known to us is that by Dr. Sharpey ; and we therefore give 

 it in his own words. 



" These," writes Dr. Sharpey, treating of the membranous tubes or 

 feet, " are very numerous, and are usually disposed in regular rows : 

 they contain a clear fluid, which is conveyed to them by a peculiar 

 system of vessels. Each foot consists of two parts, an internal and 

 generally vesicular portion placed within the body, and a tubular 

 part on the outside projecting from the surface, and continues with 

 the fit through an aperture in the skin or shell. The tube is closed 

 at the extremity, and terminates there in a sucker, which has usually 

 the form of a disc slightly depressed in the centre. Both parts of the 

 foot are evidently muscular, the fibres of the tubular portion being 

 disposed in a circular and longitudinal layer ; the cavity is lined with 

 a transparent membrane, and the tubular part moreover receives an 

 external covering from the epidermis. The foot is extended by the 

 contraction of its internal vesicle, which forces the fluid into the 

 tube ; or when a veaicle U wanting, by the projection of a fluid into 

 the tube from a communicating vessel The tubular part is thus 

 distended and elongated ; it retracts itself of course by its muscular 

 fibres ; and when this takes place the fluid is forced back again into 

 the vesicular or internal part. In progression the animal extends a 

 few of its feet in the direction in which it desires to go, attaches the 

 suckers to rocks, stones, or other fixed objects immediately in advance ; 

 then shortening iU feet it draws its body in the wished-for direction. 

 In the star-fish the feet are disposed in rows along the under surface 

 of the rays, diminishing in size as they approach the extremity. 

 There are usually two simple rows in each ray, and the vesicular part 

 is for the most part deeply cleft into two lobes, as in A. aurantiocn. 

 In other cases, as A. rubtiu, there are two double rows in every ray, 

 and each foot has a round undivided vesicle. The canals or vessels 

 which convey the fluid to and from the feet are all connected with a 

 circular vessel situated in the vicinity of the mouth. This vessel lies 

 immediately within the calcareous ring already described as connecting 

 the rays at the commencement; from it a straight canal proceeds along 

 the floor of each ray in the median line, and in its progress gives off 

 lateral branches, which open into the vesicles of the feet. There are 

 moreover connected with the circular vessel First, a certain number 

 of bodies (ten in five-rayed species) which Tiedemann compares to 

 glands ; they are very small, brown, sacculated organs, each opening 

 by a small orifice into the circular vessel : Tiedemann supposes them 

 to be the source from which the fluid filling the feet is derived. 

 Secondly, pyrifonn sacs : in A. auraniiata there are four groups of 

 thear ; and each group consists of three or four sacs, which open by a 

 common tubular pedicle into the circular vessel In some other 

 species then are five simple sacs. They are muscular, and Tiedemann 

 ooooaivM them to be the chief agent* by which the fluid is forced into 

 the vesicles of the feet, to which they are placed in a sort of antago- 

 nism. It would sMtn however that thu purpose may be accomplished 

 by other means ; for according to Heckel s statement, and we may 

 add our own observation, they are not present in all species. Lastly, 

 the circular vessel receives the singular organ named the stone-canal 

 or sand-canal by Tiedemann, who describes it as a membranous canal 

 containing a friable mass of sandy or earthy matter, which commences 

 by a wide origin on the inferior or internal surface of the calcareous 

 disc already described a* situate on the upper part of the body, 

 descends in a duplicators of fibrous membrane, and open* by a 

 narrow orifice into the circular vessel, the upper or wide end being 

 eloesd by the disc. Khrenberg has correctly remarked that this organ 

 ia not filled with an amorphous mass of earthy or cretaceous matter : 

 be describes it as exhibiting a dense network of calcareous fibres, 

 with hexagonal and pentagonal meshes, resembling in some respect* 

 the cavernous structure of the penis. The result of our own exami- 



nation, in more than one species, is different still. We have always 

 forming a jointed calcareon* tube. This 

 s of a surgeon's probe, is composed 

 of ring* of calcareous substance connected by membrane, so that 



found the earthy matter forming a jointed calcareon* tube. This 

 tube, which is about the thickness of a surg 



viewed externally it U not unlike the windpipe of a small animal. 

 On cutting it across however it U found to be more complex in struc- 



ture than appears externally ; for it contains within two convoluted 

 laminas of the same nature as iU calcareous parietes. These laminto 

 are rolled longitudinally : they rise conjointly, or as one, from the 

 internal surface of the tube, pass inwardly a certain way, then sepa- 

 rating, are rolled in opposite directions, something after the same 

 manner as the inferior turbinated bone of the ox. These internal 

 lamina) become more convoluted towards the upper end, where nt 

 last they, as well as the more external part of the tube, join the dorsal 

 disc, appearing gradually to become continuous with its substance. 

 The disc is perforated with numerous pores, which open into the 

 tube. Tiedeman conceives the function of the sand-canal to be that 

 of secreting the earthy matter required for the growth of the calca- 

 reous skeleton. Meckel considered this view as very improbable, 

 and the description we have given does not tend to corroborate it. 

 We must confess ourselves unable to offer more than mere conjecture 

 aa to the use of this singular structure. If the fluid contained in 

 the feet and their vessels be sea-water (either pure or with an admix- 

 ture of organic particles), which is probable from its chemical compo- 

 sition, may it not be introduced, and perhaps again discharged, 

 through the pores of the disc and the calcareous tube, the porous disc 

 serving as a sort of filter to exclude impurities?" (' Cyclopn 1 : . :' 

 Anat. and Physiol.') 



The reproduction of the Echinodtrmata appears to be monoecious, 

 of that nature which Professor Owen terms cryptandrous hermaphro- 

 ditism. Ovaries are, as far aa we are aware, the only organs relating 

 to the generative functions hitherto discovered ; but Fabricius, in hia 

 'Fauna Gramlandica,' would seem to affirm that two individuals are 

 necessary for the propagation of the species, and states that union 

 takes place in the month of May "congreditur oribus arete connexix, 

 altera supina." The ovaries, which appear to vary in number in 

 different species, form in general an oblong cluster of tubes branching 

 from a single stem, by which the whole is attached, and ending in cir- 

 cular dilated vesicles. In some species, Aittriat aurantiaca for instance, 

 the tubes form numerous bundles (about twenty), each of which is 

 distinctly attached, so that they are not all connected by a single 

 stem. In the Museum of the College of Surgeons, London, No. 2236 

 in a portion of a Star-Fish (A. rubrnt, Lam.) prepared to show the 

 ovaria, ten in number, attached on each side of the base of each ray, 

 near the angle of divergence ; the ova are not developed in this speci- 

 men. No. 2237 exhibits an A. pappota, Lam., with the antonm- 

 parietes of one ray and the posterior parietes of another rny, di- 

 off, showing the ovaria with the ova at the commencement of tli.-ir 

 development The ovaria are two in number in each ray, an in tin; 

 preceding species, and are similarly attached on each aide of the base 

 of the ray, where they may be distinguished from the digestive and 

 locomotive caeca by their greater opacity and granular stru 

 No. 2238 is the same species with the posterior parietes of the central 

 disc removed, showing the commencement of the digestive cmca and 

 the ovaries. No. 2239 is a portion of one of the rays of Camatttln 

 tolarit, Lam., showing the ovarian receptacles occupying the inner 

 side of each of the pinnte, or articulate processes sent off from tlio 

 rays. Three of the receptacles are laid open to expose the contained 

 ova. (' Catalogue Physiol Series.') 



M. San states that the young of A. mngtiinolrnta immediately 

 after birth have a depressed and rounded body, with four very short 

 club-shaped appendages or arms at their anterior extremity, as above 

 stated. When they are a little more developed papilla) disposed in 

 five radiating rows on the upper surface may be distinguished. At 

 the expiration of twelve days the five rays of the body, which up to 

 that time had been rounded, begin to increase ; and at the conclusion 

 of eight days more the two ranges of feet or tentncula are developed 

 under each ray, and assist in the locomotion of the animal by alternate 

 elongation and contraction and performing the office of suckers. 



The integuments of a Star-Fish are 1, a leather-like tough mem- 

 brane in which portions of calcareous matter, which may be termed 

 the skeleton of the animal, are imbedded ; 2, an external membrane 

 of a softer texture ; 8, certain appendages. " The calcareous pieces," 

 writes Dr. Sharpey, ' Cyclo. of Anat and Physiol,' " form inferiorly a 

 ring round the mouth and a series of transverse segments placed in 

 succession along the floor of each ray. The first of these segments is 

 connected with the ring ; they decrease in siite as they approach the 

 point or distal end of the ray, and openings are left between them for the 

 passage of the feet In the Aittriat rttbent, which has five rays, the 

 central ring consists of ten larger and five smaller pieces, the fonn.T 

 disposed in pairs opposite the commencement of the rays, the latter 

 corresponding to the angles between the rays. The segments of the 

 rays are symmetrical ; in the species mentioned they consist of two 

 oblong pieces united in the median line, and two smaller ones placed late- 

 rally. On the sides of the ray the calcareous substance is disposed as it 

 were in ribs ; these rise from the floor at first nearly parallel with each 

 other, and are connected by cross bars, btit on approaching the tipper part 

 or roof of the ray they cross in all directions and form an irregular 

 net-work, the intervals of which are occupied by softer integmn.-nt. 

 The ribs and bars are made up of small pieces joined by plane but 

 oblique surface*, a mode of construction calculated to admit of their 

 being lengthened and shortened upon one another, and thus to allow 

 the cavity they surround being dilated and contracted. A broad 

 calcareous disc is situated on the upper surface of the body in the 



