ECHINODERMATA .] 



MUSEUM OF ANIMATED NATURE. 



403 



pigment is reddish, and of a caustic quality, pro- 

 ducing irritation on the hands of persons rouglily 

 handhng the hving animal. The integument, coria- 

 ceous as it is, is evidently sensitive ; it shrinks on 

 the application of the knife, and the rays bend and 

 twist about in various directions. These motions 

 depend on muscular fibres or bands extending along 

 the rays from the central disc. Besides the spines and 

 tubercles, the skin of the star-fish presents numerous 

 minute polype-like processes, each having a bifid 

 or frifid point. They are termed pedicellariae, and 

 as they apply themselves to minute bodies in con- 

 tact with them, they have been regarded by some 

 as organs of prehension, but by others as distinct 

 microscopic animalcules ; the latter theory is now 

 abandoned, and the former is untenable, inasmuch 

 as the extreme delicacy of these organs ill adapts 

 them for seizing or retaining with any degree of 

 power. We are inclined to think them organs of tact. 



In the Ophiura; the calcareous plates and portions 

 are soldered and form a sort of box ; in othjer instances 

 they are conjoined by ligament; in the common 

 star-fish they form tubercles. 



If we look at the under surface of an Asterias we 

 shall perceive along each ray a calcareous frame- 

 work, composed of regular and distinct portions, 

 fitted to each other and united by ligament so as to 

 represent, in a slight degree, the vertebral column 

 of a quadruped. This arrangement commences at 

 the mouth, which is surrounded by a circular frame- 

 work of the same character, and extends in a fur- 

 row down each ray. This furrow is termed the 

 ambulacrum, or ambulacral groove. The mode in 

 which the plates of the ambulacrum are joined to- 

 gether is so contrived as to leave apertures, termed 

 ambulacral orifices, between each pair of plates, in 

 regular order. Through these orifices are protruded 

 small fleshy stems, each terminating in a sucking 

 disc. They are at once the principal organs of 

 locomotion, and of securing the prey enfolded in the 

 rays. The manner in which these suckers are pro- 

 truded and withdrawn is very curious and yet simple. 

 They are muscular and hollow, and communicate 

 with sacs or reservoirs of fluid; the walls of these 

 sacs are muscular and contractile. When the animal 

 wishes to protrude its suckers, it contracts the sacs 

 within the rays, so as to force the fluid into the hol- 

 low stems of the suckers, which, being distended, 

 emerge through the ambulacral orifices ; on the 

 contrary, when the sacs are dilated, the fluid returns, 

 leaving the tubes of the suckers, the stems at the 

 same time contracting and retiring within their re- 

 spective apertures. The fluid which these sacs con- 

 tain is supplied by a system of vessels, asserted by 

 some to be part of the vascular apparatus, but by 

 others to be totally unconnected with it. The latter 

 is the opinion of Professor Tiedemann, who, with 

 Professor Sharpey, regards the sacs of the suckers 

 as containing simple sea-water. The mouth of the 

 Asterias is seated on the under surface of the central 

 disc ; the calcareous portions surrounding it give 

 firmness, and assist in the retention of food. It 

 leads to a capacious gullet, and this into a large 

 sacculated stomach, which, instead of being con- 

 fined to the disc, is carried out by means of curiously 

 convoluted tubes through the extent of the rays. 

 These tubes are plaited on a delicate membrane 

 which both lines the external investment of the 

 animal and is reflected over all the internal organs. 

 Each ray contains two of these prolongated convo- 

 lutions of the stomach, the nature and use of which 

 do not appear to be clearly understood. Perhaps 

 they are intended for the absorption of the nutritive 

 particles of the food, which may be taken up by a 

 system of veins distributed like a fine net-work over 

 them throughout their course. They do not exist 

 in the Ophiurae, in which the stomach is plicated. 

 At the base of the stomach a biliary sac is placed, 

 opening at the former by a duct. With respect to 

 the sanguiferous system, we may observe that the 

 veins collect into a large circular vessel sweeping 

 round the circumference of the central disc; and 

 this communicates by means of a dilated vessel of 

 muscular structure and great irritability with a small 

 circular vessel running round the mouth, and which 

 is generally regarded as arterial in its functions, the 

 dilated channel being analogous to the heart. From 

 this smaller circle five tubes supply the viscera; 

 moreover, there are appended to it, at regular inter- 

 vals, certain oval vesicles containing a fluid of a 

 pale reddish tint : their use is not very apparent. 

 VVe must not here omit to notice a singular tube 

 which runs in conjunction with the vessel or com- 

 munication (or heart) between the two circles, and 

 is enclosed in the same sheath. This tube, which is 

 called the sand-canal, enters the circular oval vessel 

 by one extremity, and appears to communicate by 

 its opposite end with a calcareous nodule on the 

 dorsal surface of the disc. It is composed of a series 

 of calcareous rings : internally it contains two con- 

 voluted calcareous laminse which blend into the 

 dorsal surface. Of the use of this tube nothing is 

 definitely known. 

 Vol. II. 



The aeration of the circulating fluids in Asterias 

 is effected by a free admission of water into the 

 general cavity of the animal through multifarious 

 pores on the outer surface, bathing the viscera and 

 the peritoneal lining. This membrane is covered 

 with multitudes of minute cilia, and similar ciliae are 

 distributed over the cavities of the suckers and the 

 inside of the digestive apparatus. They are in con- 

 tinual motion, and act, it is presumed, in aiirating 

 the blood, by keeping up a continual current in the 

 water absorbed, so that every part may be washed 

 with a fresh and unexhausted portion. The nervous 

 system consists of a ring round the mouth, giving off 

 filaments to the rays and viscera. The sense of 

 touch is, in fact, very delicate in these creatures, 

 though, there being no sensorium to which sensa- 

 tions may be referred, severe wounds are endured 

 without any positive manifestation of suffering. Yet 

 the animal not only recognises its prey, when in 

 close contact, but seems aware of its presence, and 

 is attracted towards it, even at some distance. This 

 is not more wonderful than that the Hydra, which 

 may be cut asunder without injury, should feel the 

 light of the sun. Ehrenberg asserts that eyes may 

 be detected in some species, at the ends of the rays, 

 in the form of little red dots: this, to say the least, 

 is very problematical. 



With respect to the habits and manners of the 

 star-fish, we may observe that they are such as 

 may be expected from carnivorous animals. These 

 animals are among the scavengers of the sea ; they 

 devour putrescent animal substances, and make 

 shell-fish, cru.stacea, and fishes their prey. They 

 are extremely voracious, and though apparently 

 inert, are capable of overpoweiTng, the struggles of 

 the most active of their victims. When watching 

 for their prey they rest with the rays gently bent 

 towards the mouth; the instant that a shell-fish or 

 unlucky crab comes within their grasp, they fold 

 themselves closely over it, the rays pressing it to 

 the mouth, which is dilated to receive it: still it 

 might be supposed capable of escaping by the 

 exertion of strength and activity; not so, for no 

 sooner do the rays fold over it, than all the suckers, 

 to the amount of more than three hundred in each 

 ray, are protruded and fixed tenaciously upon it. 

 Its efforts are in vain, and, struggle as it may, it 

 is dragged closer and closer, and at length en- 

 gulfed. In a short time the soft parts of the prey 

 are dissolved, the hard and shelly portions being 

 rejected. Small crabs and small shell-fish are 

 swallowed entire, for the stomach is amazingly di- 

 latable ; but shell-fish of large size are not the less 

 the victims of the Asterias, though it cannot swallow 

 them whole. The destruction which it commits 

 among oysters was indeed well known to the an- 

 cients, who believed that it obtained the mollusk 

 by inserting one of its rays between the valves of 

 the shell when the creature happened to lie with 

 them partially open, and that it then gradually 

 forced itself in, till its prey became in contact with 

 its mouth. 



" Sic struit insidias, sic, subdola, fraudes 

 Stella Marina parat, sed nullo adjuta lapillo 

 Nititur, — et pedibus scabris disjungit hiantes." 



Oppian. 



That the Asterias destroys shell-fi.sh is unquestion- 

 able, but it certainly does not proceed in the mode 

 supposed by the ancients. Some degree of light 

 on this point has been the result of certain ob- 

 servations by M. Deslongchamps. On one occa- 

 sion, when the tide had ebbed, leaving only a few 

 inches' depth of water on a sandy beach, he saw 

 considerable numbers of star-fish rolling about in 

 compact balls, five or six being fastened together by 

 the interlacing of their arms. On proceeding to 

 examine these balls he found them enclosing each 

 a large bivalve mollusk (Mactra stultorum). The 

 valves of the shell were partially open, and round 

 their edges was ranged the mouth of each star-fish ; 

 while between the valves were introduced large 

 rounded vesicles t of a thin membranous texture, 

 filled with a transparent fluid. On examining these 

 vesicles more attentively, it was found that they 

 were five in number, two as large as filberts, three 

 not much larger than peas, and arose by peduncles 

 from the disc of the star-fish. From an orifice in 

 each vesicle the contained fluid oozed drop by drop. 

 When the star-fi.sh were removed from their prey, 

 these vesicles collapsed, and became no longer 

 visible. The query is, what were these vesicles ? 

 why were they introduced into the shell, and how 

 did they escape injury? The probability appears 

 to be that they contained a poisonous secretion, by 

 which the vital energies of the mollusk were de- 

 stroyed, and that they were insinuated by degrees, 

 as the mollusk, clasped in the arms of its destroyers, 

 and absorbing some of the poison poured out upon 

 the edges of the shell, became paralyzed, the ad- 

 ductor muscles losing first by degrees, then more 

 rapidly, the power of contraction, death ultimately 

 supervening. 



That this is the way in which the process was 



accomplished seems the more probable from the 

 circumstance that some of the Mactrae examined, 

 though apparently little injured, were either dead 

 or perfectly powerless. With respect to the vesicles 

 seen by M. Deslongchamps, we are not aware that 

 they have been noticed by other naturalists. The 

 use of the suckers, both in securing prey and in pro- 

 gression, has been alluded to ; by their action the 

 animal glides over the surface or up the pei-pendicular 

 sides of rocks, however smooth or slippery. In the 

 performance of this operation the rays are extended 

 to their utmost, the suckers are all jirotruded, and 

 in their movements remind one of the limbs of a 

 millipede. If one of these animals be placed in a 

 glass of clear sea-water, the curious action of the 

 suckers may be readily contemplated. 



P'rora the Stelleridie let us now pass to the 

 Echinidae, of which the Spatangus, Fig. 3778, and 

 the Echinus esculentus, Fig. 3779, are examples. 



In Echinus, the typical form, v«e are presented 

 with a subglobular box or crust, in which the ani- 

 mal is enclosed, and this box is invested with move- 

 able spines. In order to examine the box, these 

 spines (whence the animal derives the name of Sea- 

 urchin) must be removed : we shall then find it to 

 consist of numerous pieces accurately fitted to- 

 gether, their edges being adapted to each other, but 

 not soldered. These pieces or plates consist of 

 two kinds, differing from each other in size and 

 form, as well as in the design they fulfil. First, 

 then, five broad rows of large pentagonal or hex- 

 agonal rows in pairs pass vertically down the sphere, 

 forming a tessellated pavement ; we say in pairs, 

 because there are ten rows of these angular plates 

 altogether, and each is studded with an elevated 

 tubercle for the support of a spine. As the ordinary- 

 Echinus is globular or orange-shaped, these plates 

 are largest around the meridian of the globe, and 

 decrease as they approach the poles (to use figura- 

 tive language), where are seated the injestive and 

 ejestive orifices. Between these rows of tessellated 

 double plates are ambulacral bands, composed of 

 double rows of smaller plates, and pierced with 

 foramina, which give exit to hundreds of long 

 tubular suckers : now, besides these organs of pro- 

 gression, the spines of the Echinus, which differ in 

 size, form, and number in the various species, are 

 also appropriated to the same purpose. If we look 

 at the tubercles on the large plates, we. shall find 

 each surmounted by a mammililbrm apex, smooth 

 and rounded. This little eminence has a pit in its 

 centre. Now, if we take one of the spines and ex- 

 amine it, we shall find that the end which is fitted 

 to the tubercle presents a cup-like socket, with a 

 pit or little depression at the bottom. This socket 

 fits the eminence surmounting the tubercle so as to 

 form a ball-and-socket joint, and the attachment of 

 the spine is secured by a ligament (ligamentura 

 teres) which, fixed in the depression at the top of the 

 eminence, runs into the pit at the bottom of the 

 socket of the spine, thus securing it and allowing a 

 free revolving motion. A muscular capsule sur- 

 rounds this alticulation, arising from the circum- 

 ference of the tubercle, and inserted around the base- 

 of the spine ; by this capsule the spine is rotated. 

 It is by the action of these spines that the Echinus 

 buries itself in the sand: those at the poles are 

 shorter than those around the meridian, and while 

 the rest are laid flat and kept motionless, the polar 

 spines are revolved, so as to throw up the sand and 

 make a depression, into which the animal sinks ; as 

 it sinks the spines of the meridian are brought into 

 play, and then those around the mouth, the action 

 of the last-used spines being to keep an aperture in 

 the sand for the admission of water to the mouth. 

 In moving from place to place the Echinus rolls 

 along on its spines, aided by its suckers, and is even 

 able to climb rocks in quest of shells and zoophytes. 

 From the mobility of its spines and the length of 

 its suckers it is much more locomotive than its 

 appearance would at first lead one to imagine. 



The growth of the calcareous shell and spines of 

 the Echinus here demand notice. With respect tO' 

 the shell, it is lined within by a delicate vascular 

 membrane, which passes between the margins of 

 each plate so as in reality to keep them distinct, 

 and then covers the outer surface, being also con- 

 tinued over every spine. Not only the box then, 

 but its separate parts and its spines are thus enclosed 

 in a delicate skin : and to the edges of each separate 

 part this secreting membrane adds particle by par- 

 ticle, at the same time that it thickens the increasing 

 plates, and in this manner the whole enlarges without 

 any alteration of form or relative proportions. The 

 muscular capsule around the spines is only a portion 

 of this general membranous investment, which, 

 covering each spine as does a glove the fingers, 

 secretes layer after layer of calcareous matter as it 

 extends itself, and thus adds to the length and thick- 

 ness of the enclosed appendage. Thus then the 

 spines are formed by the addition of layer upon 

 layer, and a longitudinal section of one will show the 

 way in which the additions have been made. The 



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