SEA-CUCUMBERS 231 
branched respiratory trees, which are constantly supplied with 
water by the contractions of the cloaca. At the base of one of 
the respiratory trees are singular structures known as Cuvierian 
organs. They are numerous, viscid, glandular tubes, which the 
animal can throw out, and which will adhere closely to almost 
anything. The holothurian has a water-vascular system, the 
madreporic plate being near the mouth, but not opening to the 
outside, and a nervous system which starts from a ring which 
lies around the mouth. The egg-sacs are branched tubes, often 
highly colored, which open to the outside, close to the wreath 
of tentacles surrounding the mouth. 
The larve, 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 levigata 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 Téxas 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 papille. 
