473 



ECHINODERMATA. 



ECHINODERMATA. 



471 



angle between two of the rays, which is connected internally with the 

 sand-canal. The calcareous pieces are of a homogeneous structure 

 without cells or fibres ; they consist, according to Hatchett's analysis, 

 of carbonate of lime, with a smaller proportion of phosphate of lime. 

 The coriaceous membrane which connects the pieces of the skeleton 

 is made up of white glistening fibres. It is contractile and irritable, 

 for it slowly shrinks on being scratched with the point of a knife, or 

 when it is cut through. The external membrane is much thinner and 

 softer than that just described ; in various parts it is coloured, or in 

 these parts there is a coloured layer underneath it. The appendages 

 or processes on the surface of the body are of three kinds. First, 

 calcareous spines ; these are found over the whole surface, except the 

 grooves for the feet They are attached by a moveable joint at their 

 base to the calcareous pieces of the skin, and are invested by the 

 external soft membrane nearly as far as their point. Those on the 

 upper surface are solitary, short, and for the most part club-shaped, 

 their broader summit being marked with radiating points ; whence 

 they were named stelliform processes by Tiedemann. On each side 

 of the groove for the feet the spines are thickly set ; these in A. rubens 

 have three rows, in the middle and innermost of which they are 

 placed three deep. On this part of the surface they are also longer 

 and pointed. The spines are slowly moved at the will of the animal. 

 The appendages of the second kind are of a very singular nature ; 

 they have the appearance of pincers of crab's claws in miniature, and 

 were described by Muller as parasitical animals under the name of 

 Pcdicellaria. Honro gave the name of antennae to analogous organs 

 which are found on the Sea-Urchin. They probably do not exist in all 

 species, for Tiedemann makes no mention of them in his description 

 of A. aitrdntiaca. In A. rubens they cover the surface generally, and 

 form dense groups round the spines. Each consists of a soft stem, 

 bearing on its summit, or (when branched) at the point of each branch, 

 a sort of forceps of calcareous matter not unlike a crab's claw, except 

 that the two blades are equal and similar. When the point of a fine 

 needle is introduced between the blades, which are for the most part 

 open in a fresh and vigorous specimen, they instantly close and grasp 

 it with considerable force. The particular use of these prehensile 

 organs is not apparent ; their stem, it may be remarked is quite 

 impervious. The third sort of appendage consists of those which are 

 named the respiratory tubes." In the other Echinodermata the same 

 general construction of the skeleton may be observed ; but the modi- 

 fications differ with the forma. In some it consists of hundreds of 

 pieces disposed in various patterns, and fitting with the most minute 

 accuracy. In some these pieces are soldered together, as in the calca- 

 reous central purse from which the arms of the (Jphiurce radiate ; and 

 in others they are united by ligaments, as in the rays of these Opkiurce, 

 the Gorgonocephali, and the Encrinita. 



The sudden and voluntary act of dismemberment by which many 

 of the Echinodermata will save their central disc at the expense of 

 their rays or arms, must have struck those who have observed these 

 animals in their native seas, as well as the length of time during which 

 the severed parts still continue to be endowed with motion. This 

 power of dismemberment seems to be carried to its fullest extent in 

 Ophiocoma and Lttidia. The following account by Professor E. 

 Forbes of an attempt to capture a species of the last genus is a good 

 illustration of this property : 



" It is the wonderful power which the LuiJin possesses, not merely 

 of casting away its arms entire, but of breaking them voluntarily 

 into little pieces with great rapidity, which approximates it to the 

 Ophiune. This faculty renders the preservation of a perfect specimen 

 very difficult matter. The first time I ever took one of these crea- 

 tures I succeeded in getting it into the boat entire. Never having 

 Been one before, and quite unconscious of its suicidal powers, I spread 

 it out on a rowing bench, the better to admire its form and colours. 

 On attempting to remove it for preservation to my horror and disap- 

 pointment I found only an assemblage of rejected members. My 

 conservative endeavours were all neutralised by its destructive 

 exertions, and it is now badly represented in my cabinet by a discless 

 arm and an armless disc. 



" Next time I went to dredge on the same spot, determined not to 

 be cheated out of a specimen a second time, I brought with me a 

 butfket of cold fresh water, to which article star-fishes have a great 

 antipathy. As I expected, a Luidia came up in the dredge, a most 

 gorgeous specimen. As it does not generally break up before it is 

 raised above the surface of the sea, cautiously and anxiously I sunk 

 my bucket to a level with the dredge's mouth, and proceeded in the 

 most gentle manner to introduce Laiidia to the purer element. 

 Whether the cold air was too much for him or the sight of the 

 bucket too terrific I know not, but in a moment he proceeded to 

 dissolve his corporation, and at every mesh of the dredge his frag- 

 ment* were seen escaping. In despair I grasped at the largest, and 

 brought up the extremity of an arm with its terminating eye, the 

 spinous eyelid of which opened and closed with something exceed- 

 ingly like a wink of derision. Young specimens are by no means so 

 fragile as those full grown, and the five-armed variety seems less 

 brittle than that with seven arms. Like other star-fishes it has the 

 power of re-pft>dueing its arms." 



With regard to the power of restoration, few collectors have not 

 come into possession of a specimen with a budding or growing ray 



occupying the place of a lost one. [ENCRINITES.] Jussieu, Guettard, 

 and Gerard de Villars brought to Reaumur specimens of Star-Fish 

 with four large rays and a small one still growing ; tliey found others, 

 he tells us, with only three large rays and two very small ones ; and 

 others with two large rays and three very small, and, as it seemed, 

 very young ones. More than once they met with a large ray from 

 which four young rays had begun to sprout. Reaumur speaks of the 

 fact as being well known to the fishermen, and in allusion to certain 

 experiments which Jussieu and Guettard had been carrying on he 

 remarks that the portious into which they had divided the animals 

 appeared to go on well, the wounds healed and consolidated ; but he 

 adds that those who made the experiment were obliged to limit their 

 stay on the coast to about fifteen days too short a period, he 

 observes, to trace the progress of a reproduction which apparently 

 requires several months, or perhaps even more than a year for its 

 completion. 



Although the Echinodermrda have so great a power of reproducing 

 lost parts, they present no indications of any power of increasing 

 separate individuals by gemmation as witnessed in the Acalep/ue and 

 lower animals. As in the Acalephai, the embryo of the Echinodennata, 

 pass through several forms before arriving at maturity. The fol- 

 lowing is an outline of the process in the Aiteriad<s : "From the 

 accounts of the development given by different trust-worthy observers, 

 there can be little doubt that the process takes place after at least 

 two very diverse plans. The first and simplest of these has been 

 witnessed by Sars in the Eckinaster rubens ; and the observations of 

 Agassiz are on the whole in accordance with those of that industrious 

 naturalist. In the early stages the segmentation of the yoke takes 

 place as in other animals ; and the embryo comes forth from the egg 

 soon after it has attained the state of the ' mulberry mass,' aud 

 swims freely about, by means of the cilia with which it is covered, in 

 a sort of marsupial chamber which is formed by the drawing together 

 of the rays of the parent around its mouth. Soon after its emersion, 

 the embryo begins to put forth an organ of attachment, resembling 

 the stem of a Crinoid ; this at first possesses two tubercles, then three, 

 then four, with a fifth smaller one between them. At the same time, 

 the principal mass becomes flattened, and shapes itself into five lobes 

 surrounding a central disc ; thus sketching out the body aud rays. 

 When in this state it attaches itself to fixed objects by its organ of 

 adhesion ; but if detached, it swims through the water by theaction 

 of the cilia with which the body and arms are clothed ; so "that it bears 

 a strong analogy to the Pentacrimis in process of conversion into a 

 free moving Comatula. At the same time, five double rows of small 

 tubercles may be perceived radiating from the centre of what is to 

 become the ventral surface of the body; these gradually elongate 

 themselves, and become cirrhi, each furnished with a sucker at its 

 extremity. A peculiar tubercle is also seen at the edge of each of the 

 five lobes of the body ; and this is the rudiment of the ocellus, which 

 is afterwards found at the extremity of each ray. As development 

 proceeds, the primitive organ of adhesion gradually decreases iu size, 

 and the animal creeps by means of its cirrhi ; and at last the pedicle 

 is drawn (as it were) into the body, the lobes of the body lengthen 

 into rays, the animal loses its ciliograde progression, and the ordinary 

 characters of the Star-Fish become apparent The progress of the 

 internal organisation is thus described by Agassiz : ' The earliest 

 deposit of calcareous matter takes place around the prominent tuber- 

 cles of the lower surface ; at first in the condition of little isolated 

 crystals, which are formed as nuclei in the cells; and then as a 

 network formed by the coalescence of several of these. Of these 

 networks there are at first ten, symmetrically disposed on the ventral 

 surface, in a manner corresponding to the arrangement of the solid 

 plates in Crinoids ; but they gradually increase in number, and more 

 distinctly mark out the rays; new ones being interposed in pairs 

 between those already existing, and small spines projecting from the 

 older ones. The calcareous deposit in the dorsal surface, on the other 

 hand, seems to proceed from a central nucleus above the yolk-mass. 

 The progress of development is obviously from without inwards; the 

 cells on the surface of the yolk-mass being the first to undergo 

 metamorphosis into the permanent structure. Those occupying the 

 central part of the body and pedicle undergo liquefaction, and a 

 kind of circulation is seen in the latter. Gradually what remains of 

 the yolk-mass is more distinctly circumscribed in the interior of the 

 animal, and forms a central cavity with prolongations extending into 

 the rays ; but it is not until the pedicle has contracted itself into a 

 mere vesicle that the mouth is formed, by the thiuning-away of the 

 envelope of the yolk-mass on the lower surface, a little to one side of 

 the base of the pedicle ; and it is not until after the formation of the 

 mouth, that the nervous ring can be traced, with its prolongations 

 extending to the ocelli at the extremities of the rays." 



" The second plan of development seems much more conformable to 

 what will be presently described as taking place in the Opkiurida and 

 Echinidce ; for the body first developed from the embryonic mass is a 

 larva, of which little remains iu the permanent structure, and the 

 Star-Fish is budded off, as it were, from the anterior extremity of this. 

 This larva, which has received the name of Bipin-n&ria from the 

 symmetrical wing-like arrangement of its natatory organs, presents 

 much more resemblance to an Articulated, or to a Vertebrated, than 

 to a Radiated animal. Its body is elongated, and carries at its anterior 



