HOL'OTHT.PRIAN (from Lat. holo f u ri ton, Ck. (ii.,0,,61nov, water-polyp; probably from imos% /lotus. entire 4- 00iploc, fhuurios, thus h uu rus, impetuous). .111 echinoderm of the class I lot othuroidea, easily recognized by the soft body, generally worm-like form, and circle of tentacles about the mouth. The inadreporic plate is in ternal. 'Sea-cucumber.' `sea-squirt,' and 'sea-slug' are some of popular names of these animals, whose dried bodies form the Oriental (q.v.). The class have not the covering of careous plates characteristic of the more typical Echinuderniata, but a tough leathery muscular integument, in some genera strengthened by minute or rather large calcareous plates or hooks, very irritable, and cailabli. of 'great tention and Some of them are most globose, some truly worm-like; but the saw individual is often capable of extending itself to several times the length which it has in a state of repose. In the body is extended and contracted in the annelids, and in the amnions forms this is the only Ille:111:3 of locomotion, except such aid as is given by the tentacles. In the pedate forms the principal gans of loeomotion. as in starfishes and urchins, are the anibulacral feet, of which there are lines five double rows, \chile sometimes they are distributed over the whole surface of the body; but some of the species have the feet veloped only on the ventral side, and the body then presents an per nail an tinder surface. When the feet are furnished with suckers and are very extensible they are called 'pedieels,' but when they end in a blunt point and their function seems to be chiefly tory, or to serve as organs of touch, they :Ire called `papilla..' Some' hues all the feet are pedieels; sometimes there are pedieels on the tral side and papilla 20 are the usual numbers. They are very rarely short, simple, and unbranclied; generally they are provided branches which may be ar ranged along the sides, clustered at the top. or irregularly scattered. The tentacles are very
sensitive and are the most important sense-or gans of the animal; upon them are occasionally found special sense-cups, supposed to be olfactory, or there may be at the base pigment eyes or posi tional organs. The nervous system is perfectly radiate in structure and very simple in organiza tion. The mouth opens into an alimentary canal, usually much longer than the body, and therefore more or less looped or coiled. An (esophagus, stomach. intestine, and cloaca can usually be distinguished. Arising from the cloa ca, there arc often two irregularly branched or gans, known as the `respiratory trees.' These are hollow, very thin-walled, and capable of contain ing a great deal of water, which they receive through the anus. They are excretory, and per. hays respiratory in function. In many species there arise from the wall of the and extend into the body-eavity of the animal, 1111111erMIS glandular tubules, known as Utivier's organs. 'I hese can be ejected from the anus as long, sticky threads, and thus seem to be protective. The blood system is well developed in most holothu rians, especially ;thong the intestine. In those forms which have a respiratory tree one branch of it is often closely bound up with 9. network a hlood-vessels, arising from the principal vessel 011 the intestine. The sexes are generally sepa rate, hermaphrodite forms being quite unusual: but there is no external difference between male and female. save in a Very few' forms. The eggs lire generally thrown out into the water, where they are fertilized, but several viviparous forms are known. in which the („s fall into the body eavity of the mother and the young develop there. In such eases the development is direct, but in species whose eggs develop in the water the young :1 peculiar larval form, known as t e °al-feu/aria, from which the ad ults develop by a more or less com plicated metamor phosis. Several eases are known of female holothurians which brood their eggs and care for the young.