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HARfiWICKE'S^S CIE NCE-GO SSI P. 



ON THE AMBULACRAL SUCKERS AND 

 PEDICELLARI.E OF ECHINUS MILIARIS. 



By Major Lang. 



WHILST residing lately at Torquay, I carefully 

 studied the exterior organs of Echinus 

 miliar is, which is to be found there in considerable 

 abundance, under the stones at low water off Corbon 

 Head. I allude more especially to its ambulacral 

 suckers and those curious and little-understood 

 appendages, the pedicellarise. 



If a dead and dry specimen of Echinus, popularly 

 called the sea-urchin or hedgehog, is examined by 

 a novice, he is at a loss to'jmderstand how the 

 little creature is enabled to creep, as it does, under 

 and over the rocks and stones in its native element. 



Its calcareous shell is entirely covered and almost 

 hidden by sharp-pointed spines, whilst the mouth, 



ambulacral perforations that the tubular sarcodic 

 tentacles, surmounted by their sucker-like disc, are 

 attached ; each of the five plates or segments of the 

 test are covered with tubercles arranged in longitu- 

 dinal rows, the summit of each tubercle being sur- 

 mounted with a polished nipple, on which the base 

 of the spine, which is slightly hollowed out for the 

 purpose, rests, so that they form together a perfect 

 ball and socket joint, employed therefore by nature 

 long before man had ever adopted it. 



Having learnt thus much it will be well to go down 

 to the shore during low water, and obtain some living 

 specimens, which, as the creatures are tolerably 

 tenacious of life, can be brought home in some fresh 

 seaweed. A bottle of sea water must be also pro- 

 cured. On arriving at home, put the Echini in a 

 white soup plate and pour in the salt water. The 

 beautiful lilac and green tints of the spines, as they 

 languidly move in their sockets, willbe'first observed, 



Fig. 81. — PediceV.aria triphylla, &c. of Echinus miliaris. 



Fig. 82. — Pediccllaria /riiictts. a. calcareous stem, b. extensile neck, c. head. 



which is placed on the under side, is surrounded by a 

 naked membrane. But if he looks carefully with a 

 pocket lens he will perceive, between the bases of the 

 spines, and more especially between those nearest the 

 mouth and on the periphery of the buccal membrane, 

 a great number of very minute discs apparently 

 attached to or resting on the shell. These are in 

 reality the organs of locomotion, the ambulacral 

 suckers, which the animal can protrude far beyond 

 the extremities of the spines by a method which will 

 be explained presently. Now if he will rub off the 

 spines, which he can easily do, he will see that the 

 test or shell is composed of five wedge-shaped seg- 

 ments, the apices of which meet at the top, and that 

 dividing these, or joining them, if you please, are five 

 ribs, each of which is furnished with two rows of 

 puncta or holes completely perforating the shell, as 

 can be proved by simply holding it up to the light 

 and looking through its interior ; and it is on these 



and then many of the ambulacral suckers will be 

 seen extended far beyond these by their diaphanous 

 sarcodic tubes. The slightest touch will cause them 

 to retract, but with a sharp pair of scissors that por- 

 tion of the tubes beyond the spines with its suckers 

 may be cut off, the tube however shrinking up into 

 almost nothing towards the suckers. Remove this to 

 a watch glass into which a few drops of water have 

 been placed, and examine it under the microscope, 

 when it will be seen that the sucker is strengthened 

 by an interior circular skeleton, and that the tube ha& 

 fallen into corrugated folds. Replace the water by 

 some liquor potassse, and let the specimen soak in it 

 for a day or two. The potass will act upon and 

 destroy the sarcode, and a beautifully reticulated 

 calcareous disc or rosette with a scolloped margin and 

 central orifice, like a delicate piece of network will be 

 revealed, composed of from three to seven wedge- 

 shaped segments, which, if the action of the potass be 



