I I 



K.fHIXODKKMATA. 



KCIIIXODKRMATA. 



1 1 N < >I >K KM ATA. Lamarck made bin lladiaim Echinodermes 

 consist of three sections : 1st, the Stellirideans (Star-Fishes), in- 

 cluding Comatmla, Ktryalt, O,*i*ra, and AtUriat ; 2nd, Uie rAiui<r ; 

 nd 3rd, the FutuliJir. comprehending Actinia, i/ulvthiu-ia, fattUaria, 

 Priapuliu, and Stpumcultu. 



Curler' Echinodermes form hi* first class of Zoophyte*, and this 

 cLus U divided into two ordera : lit, the PedicUlated Echinodcrmi, 

 containing the great geniu Aitrriat and its aub-genera the i'xcrinitn, 

 the rtm<&r, and l/ulotlmria ; and 2nd, the Footless Echinoderms, 

 TH'lg of Holfulia. Minyai, Priapultu, the Lithoderms, .Si>iri- 

 r*lut. Ihmfllia, and TkalaMttHO, with iU aub-genera fcAiuriu and 



IV BlanriUe'i r*t*ocfenM/a are placed an hU first class of .4rli- 

 MM, and are divided into three orders : 1st JfolotkurituUa [Hoi.o- 

 THI-RIADJ:]; 2nd, JEfAimV/rofRcmninjF.]; 3r>l,.S(f/(<-ri'<ica[A8TitBlAD]; 

 embracing the Kucriaitti [EifCBixmc] ; ai well as the Free Star- 

 Fishes, Ac. 



The Ediintxlrrmata belong to the Cycloueurose sub-kingdom. 



They are characterised by poaseaaing a well-organised akin, under 

 which or attached to it are frequently found plates of solid matter, con- 

 lUtuting a kind of skeleton. They have a digestive and a vascular 

 ijmtem, and a circular nervous system baa been detected in many of 

 the species. A muscular system is constantly present. 



Before speaking of the classification of the Echinodermata, we shall 

 ix-fer generally to their organisation and structure. 



The nutritive apparatus of the EcAinodtrmata is very simple ; pre- 

 senting in most of the family a single orifice destitute of teeth in the 

 centre of the lower surface of the body, performing the functions both 

 of the mouth and the anus ; but in some presenting a digestive cavity 

 with an orifice for the evacuation of its contents, distinct from that 

 by which the food is taken in. In the ' Catalogue of the Physiological 

 Series in the Museum of the Royal College of Surgeons in London' 

 there are examples of both these modifications. 



Illustrative of the first section, consisting of those Star-Fishes which 

 have the digestive cavity simple, or without distinction of stomach 

 and intestine, receiving and expelling its contents by the same orifice, 

 we find No. 432, a preparation of a Star-Fish (Aitcricu pappoia. Linn. ; 

 SttUa Jodefoelti, Link ; Attcriai MiaHtJurida, Pennant ; Stdlonia 

 pappota, Ayr"- ; and SolatUr pappota, Forbes). It exhibits the central 

 orifice of the digestive cavity, and a portion of the integument hfta 

 been reflected on the opposite aide of the body, to show the numerous 

 caeca continued from the degestive cavity. No. 433 presents a vertical 

 section of the same species, showing the interior of the same cavity. 

 In No. 434 the integument has been removed from the whole of the 

 anterior part of the body of an Atlanta rubent, Linn. (A. glacialil 

 and A. clathrata, Penn. ; Stellonia rubtiu, Ag. ; Uratter rubent, Ag.), 

 showing the membranous digestive cavity, containing some 

 small bivalves. No. 435 is a specimen of Ailcriat diicoidea. Lam., 

 from which two rays have been removed, showing the singular 

 and beautifully ramified form of the digestive cavity. The membra- 

 nous pouches appear to be given off in two series, are sacculated, and 

 strung, as it were, upon a mesentery. 



The second modification is shown in No. 435 A, which presents the 

 body of a Star-Fish (Aletto ylacialu. Leach). Here the alimentary 

 canal is continued in a spiral direction from the cental orifice or 

 mouth, and terminates by a second direct orifice or anus, situated at 

 the extremity of a fleshy tube, which projects forward by the side of 

 the mouth. 



De Blainville states that the liver is apparent and rather consi- 

 derable in the Star-Fishes ; it occupies the circumference of the 

 stomach, forming bunches or raoemi (des espoces de grappes), \vliich 

 are prolonged morn or less into the cavity of the appendages when 

 there are any ; at least, he observes, such is the opinion of C'uvier, 

 who U followed by Spix snd Meckel. Delle Chiaje, on the contrary, 

 regards these organ* as a kind of stomachal cscca (and such an opinion 

 seems to be strengthened by the preparations above noticed), and 

 think* that the liver is an irregular organ, situated on the upper part 

 or dome of the stomach, of which no other author, according to De 

 Blainville, makes mention, snd which he himself had not observed. 

 This organ is a racemose little bag of a yellowish-green or yellow 

 colour, and iU contents present a similarity to bile both to the sight 

 and Uste. 



The very dilaUbU mouth and gullet of the Star-Fishes is admirably 



I for securing the testaceous mollusks and other animal sub- 

 i on which the family feed. When the prey U apparently dis- 

 proportioned to the parts into which it is to be conveyed, the OMopha- 

 gus or fullet, together with part of the stomach itself, can be protruded 

 and everted so as to draw the desired food into the cavity by the 

 application of the everted surface to it Thus, the shell-fish is swal- 

 lowed whole, and *(*Hilmens still living have been taken from the 

 cavity. At other times the juices of the prey are sucked out, and the 

 rxhausted bivalve is left dead with its ahsil gaping. Not that the old 

 i that the Star-Fish succeeded, in this last mode of feeding, 

 J5 a ray or finger into the gaping shell, and if it found the 

 > too strong for it, got rid of the difficulty and the ray at once, 

 OMsdous of its power of reproducing another, seems to be at all 

 founded in fact. Star-Fishes have been detected in the act of sucking 

 the juices of tWAi/rra through perforation.', and also with their 



mouths applied to the edges of the valve*. From the apparently 

 paralysed state of the bivalves fouinl in such situations, it has been 

 conjectured that the Star-Fish introduces some deleterious secretion 

 within the valves, and thus leaves the mollusk torpid and deprived of 

 tho power of closing its valves against the attacks of its dest 

 Star-Fishes are considered, and not without reason, as great enemies 

 to oyster-beds. But it is not on living prey alone that the Star-Fishes 

 feed. They seem to assist materially in cleansing the sea from dead 

 and decomposing animal matter. A human tooth has been found in 

 the stomach of a Star-Fish. 



Although there does not appear to be any special organ for respira- 

 tion in the Echinodmnata, the oxygenisation of the circulating llm.l U 

 extensively provided for by the exposure of the peritoneal cavity, and 

 all the viscera, to the sea-water, which is freely admitted through 

 membranous pipes, which have thence obtained the name of respira- 

 tory tubes. " These," says Dr. Sharpey, " communicate at their base 

 with the ulterior of the body, and are perforated at the summit by an 

 orifice which can be very accurately closed. Most of them arc placed 

 in groups or patches, and opposite each group the fibrous membrane, 

 forming the wall of the body, presents on its inside a shallow pit per- 

 forated with holes, through which the tubes communicate with the 

 internal cavity. The tubes are formed externally of the superficial 

 layer of the skin, and ore lined in the inside by a prolongation of the 

 peritoneal membrane. This membrane lines the parietes of the b...ly, 

 and is reflected over the contained parts ; at least it covers the t 

 and crccn, snd probably also the ovaries and vesicles of the feet ; \< \ < > - 

 site the perforated pita it sends prolongations through the holes into 

 the tubes, as may be easily seen on stripping off a portion of it 

 There can be no doubt that sea-water enters tho peritoneal cavity. 

 The animal slowly distends itself with that fluid, and again, but at no 

 stated interval, gives out a portion of it This is obvious from the 

 fact that the some animal may be seen distended at one time and 

 flaccid at another. Naturalists are generally of opinion that the water 

 enters and issues by the respiratory tubes, and indeed no other orifices 

 have been discovered. We must however freely own that we have 

 never been able actually to observe its passage through these tubes. 

 The peritoneal membrane seems to be tho principal seat of respira- 

 tion ; spread over the viscera and the parietes of their containing 

 cavity, and lining the respiratory tubes, it presents a great extent of 

 surface continually in contact with the surrounding medium ; and we 

 have found that a beautiful provision exists for maintaining currents of 

 water along the membrane, and thus effecting that constant renova- 

 tion of the fluid hi contact with its surface, which is required in the 

 respiratory process. These currents are produced by means of cilia. 

 Ciliary currents take place also on the external surface of the body, 

 which probably partakes in the process of respiration. We Imvo 

 moreover observed them within the tubular feet, and on the internal 

 surface of the stomach and case*. In this hist situation they arc pro- 

 hably subservient to digestion." (' Cycloptedia of Anatomy and 

 Physiology.') 



Tiedetnanu and Delle Chiaje are the authorities from win mi a 

 knowledge of tho circulating system of these animals is principally 

 derived ; but this part of their organisation is so obscure, that we 

 need not be surprised at the difference which exists in tho views of 

 those observers. Thus, the true sauguifurous system is, according to 

 Ticdemanu, restricted in a great measure to the alimentary organs 

 and ovaries, and he consequently supposes that the ducts which con- 

 vey the fluid supplied to the feet afford nutrition to other parts of 

 the body. In other words, he recognises two distinct system- "f 

 nutrient vessels ; one a true sauguiferous system, consisting of vessels 

 which carry blood, ami the other a set of Teasels (those of the feet) 

 conveying a nutritious fluid secreted from the blood. 



Delle Chiaje contends that the two orders of vessels above alluded 

 to intercommunicate, and so form but one system. 



1 >i . Sluirfiey is disposed to conclude, from his own observations, 

 that the vessehi of the feet form a system apart from the blood-vessels, 

 as Tiedemann maintained ; but he observes that there is considerable 

 reason to doubt whether, as that author supposes, they serve an the 

 nutritious vessels of the parts in which they run ; for, according to 

 Tiedomann's description, it does not appear that they ramify in the 

 tissues. Moreover, Dr. Sharpey adds, their contained liquid docs not 

 present the usual characters of blood, or of a fluid adapted to nourish 

 the textures. He admits it to )>e true that there are floating particles 

 suspended in it, but he states that the clear fluid, when filtered, yields 

 no trace of animal matter, but agrees a! y in composition 



with sea-water. Such, at least, was the result of Dr. Sharpey's 

 examination of it in the Attrricu ; and he proceeds to give an account 

 of the proper sanguiferous system, following Tiedemann as his leading 

 authority, but, at the same tiino, stating the more material points in 

 which Chiaje differs from him, thus 



" In Attrritu, a delicate vessel runs along the upper surface of each 

 of tho ctccs. There are, of course, ten such vessels in A . aurantiaca 

 (from which the description is taken), corresponding in number with 

 the ones. They commence near the extremity of the rays, and, 

 receiving branches from the branches and lobes of the cecca, proceed 

 to the central part of the animal, where they terminate in a circular 

 vessel which runs round the upper part of the body on the internal 

 surface. The circular vessel also receives ten branches from the 



