236 GENERAL ZOOLOGY 



ing tentacles. Internally there is a water- vascular system 

 with a ring canal and radial canals. In respiration water is 

 drawn into the intestine at the aboral end, and an exchange 

 of gases takes place through internal gills that join the 

 intestine. 



The tentacles in the picture are not extended in the usual 

 radial direction. The reason is that when photographed the 

 animal was using its tentacles as well as its tube feet to 

 crawl along the bottom of a dish of sea water. When the 

 animal is at rest the tentacles are probably used to capture 

 small animals and to pass them to the mouth. 



Relatives of Cucumaria have been known by observers 

 to disgorge the entire set of internal organs through the 

 mouth opening. In captivity they appear to do this when 

 placed in unfavorable situations. It is not so remarkable 

 that they should lose their internal organs, as it is that they 

 should regenerate them all again as perfect as ever. If sea 

 cucumbers throw out their internal organs in nature, it 

 would appear to be a very expensive process. Since they do 

 perform this action, in nature as well as in captivity, there 

 must be some reason for it. The only reason that suggests 

 itself is based on the fact that fish prey upon sea cucumbers. 

 The sea cucumber is a slow-moving animal, and once seen 

 by a roving fish the chances of escape under ordinary cir- 

 cumstances would be few indeed. If the prospective victim 

 when disturbed were to eject its internal organs into the 

 water, the fish, true to the instinct of its kind, would gobble 

 up the swiftly moving object, and probably go away 

 satisfied. 



Sea cucumbers are prepared and used as food by the 

 Chinese, and it is reported that the Siwash Indians of the 

 northwest of the United States eat them, and sea urchins 

 also. 



