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 larvae, when free-swimming, are called Auricula. In the 

 deep-water species, Cucumaria crocea and Psolus epliippiyer, the 

 eggs, when discharged, and the young are carried on the back of 

 the mother. In Cucumaria Icwigata 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. 



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 papillae. 



