on the dorsal; rare ly all the feet are In f a in ilies the feet are completely want The radiate structure is apparent at the mouth, which is surrounded with tentacles, in number frequently a multiple of tive, exhibiting considerable variety of form. and capable of being more or less retraeted. These tentacles vary in number from S to 30, but It), 1•, 15, and The holothurians are capable of the most extra ordinary regeneration of parts, even of the most important organs. direct relation with this is their curious and noteworthy habit of eviscera tion. Alany species when alarmed or irritated ex pel from the anal opening (or less commonly the mouth) the viscera, either wholly or in part, They thus lose their entire iligestive,reproductive, respiratory, and excretory systems and a ]:urge part of the blood system; but if not disturbed further, they will, in the (-nurse of a few weeks, replace all they lost with an entirely new set.
Holothurians are found in all seas, but par ticularly abound in the West Indies and between Asia and Australia. The largest American spe cies is llolothuria Floridana, which abounds just below low-water mark on the Florida reefs. An other large one, Cueumaria frondosa, inhabiting the North Atlantic, and probably circumpolar, is about a foot in length, and is yellowish-brown. a\lany of the tropical species exhibit attractive colors, and are among the creatures which make the bottom of the sea, particularly among coral reefs and islands, extraordinarily interesting.
The holothurians (11olothuroidea ) are classified in two orders according to the point of origin of the tentacles. In the Actinopodu they arise from
the radial vessels of the water-vascular system, while in the Paractinopoda they arise from the eireumoval ring. The Aetinopoda include more than five-sixths of the species, and are grouped in five very distinct families. Of these, the Ela sipoda are the most remarkable. They are all deep-sea forms and occur in all parts of the world. ',Many of them assume the most grotesque shapes. and some reach a large size. The Parae tinopoda arc all footless forms, of a single fam ily. The best-known genus is Synapta, contain ing more than fifty species found in all parts of the world. About six hundred species of holo thurians are known, varying in size from :those half an inch long up to certain tropical species two or even three feet in length. The colors vary from white, or almost transparent, to jet-black. but as a rule the colors are more or less in correspondence with the bottom on which the animal lives. 'They chiefly feed on Foraminifera. Their movements are generally very sluggish, and they seem to have few enemies. All are barmles4, but the only ones of any use to man ate the larger forms, from which Ikebe-de-mer, Or trepang, a great delicacy with the Chinese, is prepared.
Consult; Ludwig, "Die Seewalzen." in Brown, Klassen and Ordnungen des Tierreichs: Eehino dermen, yol. i. (Berlin, 1889-92), the standard work on holothurians; Lampert, Die Seewalzen (Wiesbaden, 1885) ; the best work in English is The61, "Report on the Ilolothuroidea." in Chal lenger Reports: Zoology. vol iv., part 13. and vol. xiv., part 39 (London, 1882 and 1886).