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THE AMERICAN NATURALIST [Vol. XLVIII 



August 2.— It is now oriented with respect to the direction of the 

 light and has reached probably the darkest portion of the jar. 



August 7.— Has advanced still farther. Came about half way out of 

 the sand to do this. 



August 8— Reacts quickly to shadows by withdrawing, and to jar- 

 ring the table. Evidently is recovering its normal behavior. 



August 10. — Has again come up about half way out of the sand. 

 Reacts quickly to shadows as before. 



August 11.— Came entirely out of the sand. Spent the day on the 

 sand or on the side of the jar. Appeared restless. 



August 12, 4 p.m.— Has been clinging to the side of the jar and mov- 

 ing about more or less all day. Respiratory movements are strong and 

 apparently normal. Has just now expanded the anterior end suffi- 

 ciently for me to see the new growth of tissue formed around a penta- 

 gonal opening. Fifteen minutes later it was observed to extend a set of 

 minute tentacles and go through feeding movements. The tentacles ap- 

 peared to be slightly more than three eighths of an inch in length. Its 

 behavior continued apparently normal until it was killed twelve days 

 later. 



The actions of other Thyone were studied under the 

 same conditions, and we shall now give a general sum- 

 mary of their behavior during regeneration. The earli- 

 est reactions after evisceration take the form of contrac- 

 tions resulting in the closure of the wound, and move- 

 ments in response to lack of oxygen. If the oxygen 

 supply is sufficient Thyone will draw itself closely into 

 the angle between the side and bottom of the aquarium, 

 or if the supply is deficient, it clings close to the side of 

 the jar near the surface. In from three to seven days 

 an instinct to burrow usually asserts itself. There is a 

 tendency for the body to contract very noticeably at this 

 time, and the whole organism becomes rather inactive. 

 This condition is probably necessary for the formation 

 of new tissue. Pearse makes the statement that in bur- 

 rowing the normal Thyone will cover itself in from two 

 to four hours. My observations on the mutilated ani- 

 mals indicate that they require from twelve to twenty- 

 four hours, in one case forty-eight hours, to complete the 

 reaction. The process frequently stops for some hours 

 and occasionally is never completed. In the Thyone de- 



