PEDICELLATA. 641 



penetrate into the cavity. Rotula has one of the margins toothed like a wheel ; and some have large pores, and 

 some not. 



Cassidulus, are oval, with the vent above the margin on one side, and the lines of pores incomplete. They are 

 distinguished by the number and extent of the lines of pores, which in some species form only a rosette on 

 the back. 



Clypeaster, have the vent near the margin, the body depressed, the base concave, and the outline sometimes 

 angular and sometimes round. 



Fibularia, small in size, mostly globular, with the openings on the under side, and a rosette of pores above. 



Spatangiis, have the openings below, and the rosette on the back. Some have the outline round or oval, and 

 sometimes with a deep groove on one side, making the section heart-shaped. 



Of the last, two specimens are found in the European seas; and the last, especially, has branched tentacula 

 surrounding the mouth, in which character it bears some resemblance to Holothuria. The other irre^-ular ones 

 are chiefly fossil, and aboimd in various marine strata, especially in the chalk formation. 



THE THIRD FAMILY OF THE PEDICELLATA. 

 The Holothuria (Sea-slug). 

 These have the body oblong, with a leather-like covering, and an aperture at each end. The mouth 

 is without teeth, or has only bony plates instead ; but it is surrounded by curiously-branched tenta- 

 cula, M^iich the animal can, at pleasure, retract entirely ; and it is also furnished with sacs for the 

 secretion of saliva. The reproductive organs are also situated near the mouth, composed of a number 

 of ramified culs-de-sac, all opening into one oviduct. The impregnating parts are understood to be 

 some very elastic chords near the other extremity of the animal ; thus each individual is bisexual. 

 The intestine is long, convoluted, and fixed to the covering of the body by a kind of mesentery. 

 Along the intestine there is also a double system of complicated vessels, which appear to be the organs 

 of circulation. The opposite extremity is not less curious ; for, besides the vent, it contains the respi- 

 ratory organ, or gill, which is in the shape of a hollow tree vei7 much branched, and the animal can 

 receive or expel water by means of this apparatus, which possibly thus assists it in its locomotion, as 

 well as supplies air from the inhaled water. In the breeding season the ovaries become very much 

 extended, and contain a reddish matter, which is understood to be the spawn, or eggs. These animals 

 are exceedingly sensitive, as is the case with the Leeches among Annelidx ; and when disturbed, they 

 sometimes contract so violently that the integuments are ruptured, and the intestines protrude. The 

 subdivisions are made according to the arrangement of the feet. 



Thus, in some, as in H. phantapus, which inhabits the European seas, and has the body almost scaly, all the feet 

 are on a soft disc in the middle of the body ; and when they crawl, the extremities are turned up. When extended, 

 the tentacula of these are very large. 



Some, as //. squamata, a small species of the European seas,— but there are much larger ones in hot climates,— 

 have all the under surface soft, with numerous feet ; and the upper surface convex, sometimes supported by bony 

 plates, and the opening of the mouth in the form of a star. 



In others, again, the body is cartilaginous, flattened horizontally, and sharp at the edges, with the mouth and 

 feet on the inferior surface. Of these, H. regalis, found in the Mediterranean, is more than a foot long, three or 

 four inches broad, and crenulated at the edges. 



Others still, have the body cylindrical, and capable of being inflated with water. All the under side is furnished 

 with feet, and the remaining parts roughened in various ways. //. tremula, common in the European seas, the 

 Mediterranean especially, is an instance of this peculiarity of form. It :s of a black colour ; more than a foot 

 long when inflated with water ; has the back bristled with soft conical points, and the mouth furnished with twenty 

 branched tentacula. 



Yet, in others, the feet are arranged in five rows, like the ridges on a melon, of which the European species, 

 H. penacta, is more than a foot long, and of a brown colour. 



There are also some, as H. papulosa, which have the body equally furnished with feet round its whole surface. 



[The HolothuricB of the European seas, even of the Mediterranean, are not very numerous, neither 

 are they brilliant in colours ; but in more tropical seas, where coral reefs rise within a moderate distance 

 of the surface, as in the Red Sea, and the seas to the north and east of Australia, they are exceedingly 

 numerous, and many of them splendidly coloured ; so that, together with other Radiata of this and of 

 other orders, they make the sea-bottom, when seen by the light of an almost vertical sun, as gay as a 

 tropical garden. The Holothuria; resemble cucumbers ; and various Actiniae, when their tentacula are 

 expanded, have as gay an appearance as the flowers of almost any plants. Many of this species are 

 esculent, and of a very gelatinous nature. When properly prepared, the Chinese are exceedingly foncl 



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