[Illustration: Internal organs of a /Holothurian/, as seen when the body-wall is divided along the middle of the dorsal surface: /b.w./, body-wall; /circ. mus./, circular layer of muscle; /cl./, cloaca; /cl. op./, cloacal opening with five teeth; /cuv. org./, Cuvierian organs; /gen. ap./, genital aperture; /gen. du./, genital duct; /gen. gl./, genital gland; /int./, intestine; /inter. oss./, interambulacral ossicles; /int. ves./, intestinal vessels; /long. mus./, longitudinal band of muscle; /mad. can./, madreporic canals; /mes./, mesentery; /pol. ves./, Polian vesicles; /rad. amb./, radial ambulacral vessel; /ri. bl. ves./, ring blood-vessel; /resp./, respiratory trees; /ring-ves./, ring-vessel of the ambulacral system; /stom./, stomach.] The larvæ, when free-swimming, are called /Auricula/. In the deep-water species, /Cucumaria crocea/ and /Psolus ephippiger/, the eggs, when discharged, and the young are carried on the back of the mother. In /Cucumaria lævigata/ there is a brood-pouch, while in /Synapta viviparia/ the young develop in the body-cavity. The holothurians have the singular power of ejecting the whole of their internal organs and of growing them again in case they escape the enemy they have endeavored to elude by this strange method. They also turn themselves inside out, as it were, as if from /nausea/, when confined in water too stale for their uses. Often the viscera are ejected through holes in the sides of the body broken by violent muscular contractions. Holothurians are generally distributed through all seas, but are congregated in greatest numbers in Eastern seas. Their habitat extends from shallow to very deep water. They are found in tide-pools, on rocks, and in sand or mud. Like worms, they live on organic particles contained in mud and sand, which they take into the gullet and pass through the alimentary canal. ORDER =PEDATA= GENUS ^Thyone^ ^T. briareus.^ This is a large purple holothurian, found in shallow water from Texas to Cape Cod. It is four to five inches long and one inch or more thick, purple in color, and thickly covered over its whole surface with prominent papillæ. [pg232] GENUS ^Pentacta^ [Illustration: /Pentacta frondosa/, the sea-cucumber.]