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THE AMERICAN NATURALIST [Vol. XLVIII 



EviSCEKATION 



Only one method of producing evisceration was used. 

 By placing a number of Thyone in a small aquarium of 

 stagnant sea water, the supply of oxygen is soon ex- 

 hausted. The animals become greatly distended, they 

 crawl up on the sides of the aquarium when possible, and 

 extend the siphon toward and frequently above the sur- 

 face of the water. All of their behavior, including the 

 pumping of the siphon, indicates that respiration is in- 

 adequate. In the course of a day or two the water be- 

 comes very foul ; soon some of the Thyone will eviscerate, 

 and a considerable percentage will do so as conditions 

 grow more unfavorable. Many, however, resist the un- 

 favorable surroundings and will not eviscerate though 

 kept for several days in foul water. But if the aquarium 

 is now placed where it will have a continuous stream of 

 water and air bubbles passing through it, the behavior of 

 the animals is somewhat different. They then tend to 

 contract to a minimal size, and sometimes assume a 

 volume not more than one fifth to one seventh of their 

 maximum distention. The respiratory movements are 

 practically discontinued; the animal seeks a position as 

 close as possible to the side and bottom of the aquarium. 

 Contraction does not always take place immediately. To 

 my surprise, after several hours I found Thyone which 

 had resisted the previous unfavorable conditions now dis- 

 charging their viscera. After remaining two or three 

 days in the running water, and the animals had appar- 

 ently become adjusted to this condition, I again set the 

 aquarium to one side partly filled with water. Then, by 

 repeating the conditions of the first experiment, as the 

 water became foul several more of the holothurians ap- 

 parently found life too strenuous to further retain their 

 internal organs. When the remainder of this lot of 

 Thyone was returned to running water, and again to 

 stagnant water, a few additional individuals underwent 

 self-mutilation. Out of a total of sixty-one specimens 

 used in this lot forty of them eviscerated. That is, autot- 



