The Holothuriæ found under stones at low spring tides, on the British coasts, are small; those dredged up from deep water are five or six inches long, and not unlike a well-grown warty cucumber; they do not form an article of food in Europe, but they are highly esteemed by the inhabitants of the Indian Archipelago and in China, where many shiploads of the trepang are imported annually. It is a species that swarms in the lagoons of the coral islands, the reefs of the coral seas, and at Madagascar. Some species are two feet long, and six or eight inches in circumference. The order of the Holothuridæ form eggs like all the other Echinoderms; the larval zooid has the same form as that of the star-fishes, and changes its form twice, while the members of the Holothuria are forming within it; at last they combine with those of the zooid, and no part is cast off. _Echinodermata Synaptidæ._ The Synaptidæ are five-sided creatures, similar in structure to the Holothuriæ, though more worm-like. The whole order, which consists of the two genera of Synapta and Chirodota, have twelve calcareous plates round the mouth, five of which are perforated for the passage of the vascular water canals, which convey the liquid for the protrusion of the feet. [Illustration: Fig. 144. Skeleton of Synapta.] The calcareous particles imbedded in the skin of the genus Synapta are anchor-shaped spicules fixed to elliptical or oval plates, (fig. 144). The plates are reticulated and sometimes leaf-shaped, and the flukes of the anchors are either plain or barbed. All the anchors are fixed transversely to the length of the animal, lying with great regularity in the interspaces of the longitudinal muscular bands. Sometimes a thousand anchors are crowded into a square inch, each elegant in form, perfectly finished, and articulated to an anchor-plate, whose pattern as well as that of the anchor itself is characteristic of the species to which it belongs. In the Synapta digitata, which has four fingers and a small thumb on each of its twelve oval tentacles, the anchors are but just visible to the naked eye;[36] in all the other species they are microscopic. Besides the anchors, the skin of the genus Synapta contains innumerable smaller particles, ‘miliary plates,’ which are crowded over the muscular bands. The muscular system of the Synapta digitata is so irritable that, on being touched, it divides itself into a number of independent fragments, each of which keeps moving for a time, and ultimately becomes a perfect animal like its parent. Specimens of this Synapta have been found on the southern coasts of England and in the West of Scotland, but the genus is rare, although containing several species in the British seas; it is more common in the Adriatic; but they cannot be compared, as to size, with the great Synapta of Celebes, which is sometimes a yard in length, and is known among the natives as the Sea Serpent.