I'-'' 



ECHINODERMATA. 



ECHIXOBERMATA. 



470 



ovaries, and five from the stomach, which, before joining it, unite into 

 two. The vessels described seem to constitute the venous system, 

 and Tiedemann further supposes that the csccal and gastric veins 

 convey the chyle or nutritious part of the food from the alimentary 

 organs. The circular vein opens into a vertical canal, which descends 

 along th'i prominent angle between the two rays, inclosed in tha same 

 membranous sheath with the sand-canal, and terminates in an inferior 

 circular vessel. The descending canal is dilated in the middle ; its 

 comparatively thick brown-coloured parietes are smooth externally, 

 but reticulated on the inside, and composed of interlaced fibres, which 

 Tiedemann found to possess muscular irritability. He accordingly 

 considers this canal as the heart. The inferior circular vessel (which 

 must not be confounded with the circular canal connected with the 

 feet) surrounds the mouth on the outside or inferior surface ; it sends 

 out five branches, which pass into the interior of the body, and are 

 distributed to the stomach, caeca, and ovaries. Tiedemauu regards 

 these branches, with the circular vessel from which they proceed, as 

 arteries, and he thinks it probable that their minute ramifications 

 open into the radicles of the veins, though from their delicacy he has 

 not len able to ascertain the fact by injection. Tiedemann's view of 

 the function of the respective vessels is derived solely from a consi- 

 deration of their anatomical disposition ; and while in the same way 

 it may be inferred that the blood circulates iu a direction conformable 

 with this view, it must nevertheless be kept in mind that no direct 

 7>hysiological proof of such a course of the blood has been yet obtained. 

 Besides the vessels described, Tiedemann found yet another circular 

 vessel surrounding the mouth on the under surface, and placed more 

 superficially than the last mentioned ; it is of an orange colour, and 

 sends a branch along each of the rays in the groove which is on the 

 middle of their inferior surface. He could trace no connection 

 between this vessel or iU branches and the rest of the vascular 

 system, and he professes himself at a loss to conjecture what may be 

 its function. 



" According to Delle Chiaje, the circular vessel into which the canals 

 of the feet open receives also the veins from the upper surface of the 

 ceeca and stomach. The same vessel, which he names the venous 

 sinus, gives out 1, twenty short dental arteries; 2, the mesaraics to 

 the under surface of the ctcca ; 3, five vertebral arteries which open 

 into the vesicles of the feet ; 4, the radial to the under part of each 

 ray ; 5, the dorsal arteries to the upper part of the ray, which extend 

 their ramifications to the external surface of the body." (' Cyclopasdia 

 of Anatomy and Physiology.') 



Professor Owen, in his Preface to the third volume of the ' Descrip- 

 tive and Illustrated Catalogue of the Physiological Series of Compa- 

 rative Anatomy contained in the Museum of the Royal College of 

 Surgeons in London,' remarks, that when the nervous system begins 

 to be distinctly eliminated in the form of fibres, it is accompanied by 

 a distinct development of the muscular system; and the digestive 

 canal is provided with a proper contractile tunic, and floats freely in 

 an abdominal cavity. He observes that the nervous fibres in the 

 classes of animals iu which they are first discernible proceed from a 

 ganglion or ganglions in the neighbourhood of the mouth, and extend 

 in a radiated or longitudinal direction according to the form of the 

 body, but are not afterwards brought into communication by gan- 

 glionic masses. 



" The Echinodermx, as the Star-Fish and Sea-Urchins," writes the 

 Professor, " first present these conditions of the nervous, muscular, 

 and digestive systems. A very gradual transition from the radiated 

 to the elongated form is traceable from this class through the Hnln- 

 tkuriir and Si/iuncali to the cavitary Entozwi or VirMminthn (intestinal 

 worms having an abdominal cavity), and thence to the Epizoa and 

 Rolifera, which make a near approach to the annulose division of the 

 animal kingdom ; but at the same time do not possess that structure 

 of the nervous system which is its true characteristic. The four 

 classes of animals, thus distinguished by a common character of the 

 nervous system from the Acrita on the one hand, and the Articulata 

 on the other, constitute a second division of the animal kingdom, which 

 may be termed Protoneura." 



The preparation No. 1292 A, in the series illustrative of the nervous 

 system of the Neinatoneura is a Star-Fish (Asteriat papptaa, Lam.) 

 with the membrane removed from the oral surface of the central disc, 

 to show the simple nervous chord surrounding the mouth and distri- 

 buting filaments to each ray. These filaments run in the interspace 

 of the tubular feet, extending from between the spines which protect 

 the ambulacral grooves. (' Catalogue.') 



Tiedemann, who discovered the nervous system in these animals, 

 describes it in Aiteruu auranliaea as composed of a delicate white 

 chord surrounding the mouth, in form of a ring immediately on the 

 external side of the circular vessel into which the heart opens, and of 

 filaments arising and diverging from the annular chord opposite to the 

 ry three filaments for each ray one running along the under sur- 

 face in the median line, and appearing to send small branches to the 

 feet ; the other two, shorter, passing between the first and second 

 segment of the ray into the interior of the body, and probably dis- 

 tributed over the stomach. No ganglia were discovered by Tiede- 

 mann, but minute ganglia have been described by others as existing 

 at the points whence the diverging filaments spring. (Grant's ' Comp. 

 Anat.') 



All of course agree in assigning the sense of touch to the Star- 

 Fishes, but many would confine their endowment to that sense. 

 Professor Ehrenberg however, who is a keen and accurate observer, is 

 disposed to think that some of them at least are gifted with visual 

 organs under the form of a single red speck at the termination of each 

 ray. These specks had been long noticed, but without any determinate 

 conjecture as to their use in the animal economy, till he, struck by 

 their outward resemblance to the eyes of the Entomoslraca and Infu- 

 soria, thought that they might be organs of sight, and he traced the 

 long nerve of the ray up to the extremity, where it enlarges into u 

 sort of ganglion connected with the red speck. 



Professor Rymer Jones, after noticing the nervous system of these 

 animals, thus expresses his dissent from Professor Ehrenberg' s views : 

 " Such an arrangement can only be looked upon as serving to asso- 

 ciate the movements performed by the various parts of the animal, for 

 no portion of these simple nervous threads can be regarded as being 

 peculiarly the seat of sensation or perception. But this inference is 

 not merely deducible from an inspection of the anatomical character 

 of the nerves : it is based upon actual experiment. We have fre- 

 quently, when examining these animals in a living state -that is, when, 

 with their feet duly developed, they were crawling upon the sides 

 of the vessel in which they were confined cut off with scissors suc- 

 cessive portions of the body so as to expose the visceral cavity ; but 

 so far from the rest of the animal appearing to be conscious of the 

 mutilation, not the slightest evidence of suffering was visible : the 

 suckers placed immediately beneath the injured part were invariably 

 retracted ; but all the rest, even in the same ray, still continued their 

 action, as though perfectly devoid of participation in any suffering 

 caused by the injury inflicted. Such apathy would indeed seem to be 

 a necessary consequence resulting from the deficiency of any central 

 seat of perception whereunto sensations could be communicated ; 

 nevertheless Ehrenberg insists upon the existence of eyes in some 

 species of the star-fish, attributing the function of visual organs to 

 some minute red spots visible at the extremity of each ray, behind 

 each of which he describes the end of the long nerve which runs along 

 the ambulacral groove as expanding into a minute bulb. We must 

 however confess that the proofs adduced- in support of such a view of 

 the nature of these spots appears to us t% be anything but satisfactory ; 

 and as we have already stated in the first chapter the physiological 

 objections which may be urged against the possibility of any localised 

 organ of sense being co-existent with a strictly nematoneurose con - 

 dition of the nervous system, they need not be repeated here. The 

 general sense of touch in the Astefidce is extremely delicate, serving 

 not only to enable them to seize and secure prey, but to recognise its 

 presence at some little distance, and thus direct these animals to their 

 food. A person who has been in the habit of fishing with a line in the 

 shallow bays frequented by star-fishes, and observed how frequently 

 a bait is taken and devoured by them, will be disposed to admit this ; 

 yet to what are we to attribute this power of perceiving external 

 objects ? It would seem most probably due to some modification of 

 the general sensibility of the body, allowing of the perception of im- 

 pressions in some degree allied to the sense of smell in higher animals, 

 and related in character to the kind of sensation by which we have 

 already seen the Actinue and other polyps able to appreciate the pre- 

 sence of light, although absolutely devoid of visual organs." ( ( General 

 Outline of the Animal Kingdom and Manual of Comparative 

 Anatomy.') 



Professor Edward Forbes, although he admits that the existence of 

 ganglions in the nervous system of these auimils is generally regarded 

 as doubtful, seems, from the frequent recurrence of the terms ' eye ' 

 and ' eyelid,' to be of opinion that the specks above alluded to arc 

 visual organs. (' History of British Star-fishes and other Animals of 

 the Class Echinodermata.') 



Our own opinion and observation are in favour of the views of 

 Ehrenberg ; and we think that those who have accurately watched 

 the Star-Fishes which are furnished with these specks on the sea-coast 

 will in general be irresistibly led to the conclusion that the organs, 

 though not eyes in the strict sense of the term, serve the purposes of 

 vision modified to the exigencies of the animal, enabling it to seek or 

 avoid objects according to its will. Nor does analogy, in our view of 

 the case, present any difficulty. We have only to consider that the 

 centre is a head as well as a stomach, a condition that will hardly be 

 denied to it, and the rays proceeding from it may be viewed as so 

 many antennrc (take those of the snail for example, with their ter- 

 minal ocular points, as in some degree analogous) -with visual dots 

 at their extremities. This, at all events, may solve the problem of 

 the destructive visitation of these animals to the baited line, more in 

 unison with the analogies than the supposed existence of a general 

 olfactory sense, of whose presence not the slightest trace has been 

 observed. 



The muscular system is generally present in the EMnodermata, 

 but the organs of motion in them are various. The rays themselves 

 are moveable, and in the free forms aid in the removal of the animals 

 from place to place. Thus the common Star-Fish can bend its rays 

 towards the upper or towards the lower surface of the centre or disc, 

 and can approximate some while it extends others ; so that they are 

 widely divaricated laterally, and thus facilitate its advance in the 

 water, or its passage through small spaces. In the common Star-Fish 



