18 



Exper. no. 6. Each of fifteen individuals was divided longitudi- 

 nally into two equal parts and all organs were removed. 



Exper. no. 7. Fifteen individuals were cut open along an inter- 

 radius from oral to aboral end, but no organs were removed. 



Exper. no. 8. Thirty individuals were cut into two. parts longi- 

 tudinally in such a way that the lantern was divided into equal or 

 nearly equal parts, and each part contained one-half of the cloaca and 

 one respiratory tree. All parts of organs were left in each of the pieces. 



Exper. no. 9. Each of fifteen individuals was first divided trans- 

 versely into two equal parts ; then each part was split longitudinally and 

 all organs except the cloaca removed. The cut edges were then sewed 

 together. 



Exper. no. 10. In five individuals 2 cm of the length of a radius 

 was removed. 



Exper. no. 11. In five individuals 2 cm of the length of an inter- 

 radius was removed. 



Exper. no. 12. In five individuals a piece of the body-wall 1 cm 

 wide, was removed across one radius and one interradius. 



Exper. no. 13. In five individuals, the skin on the anterior end of 

 the animal was cut off so that the calcareous ring 2)rojected somewhat 

 but no tentacles, and no internal organs were removed or injured. 



Experiments similar to those enumerated above were carried out 

 with other species of Dendrochirota, with the Aspidochirota, and with 

 the Synaptidae. A discussion of the results for these forms is reserved 

 for a later publication. 



Results for Thyone briareus and for Cucumaria gruhi. 



In Thyone briareus and in Cucumaria grubi, a contraction of the 

 body-wall immediately follows the operation so that each piece into 

 which the body of the animal has been divided, becomes- shorter and 

 thicker. The cut edges draw together from all sides of the circular 

 aperature until the opening is entirely closed. This contraction lasts 

 about twenty-four hours, when a relaxation sets in so that in some cases 

 portions of the internal organs protrude through the opening. When 

 a part of the intestine projects, it sometimes becomes large and bladder- 

 like, as if inflated with air or filled with water. The animal may remain 

 in this condition during "several weeks after which the organs are with- 

 drawn into the body; the opening is closed either by the formation of a 

 somewhat circular area of new tissue as in Cucumaria, or by having the 

 walls firmly knit together as in Thyone. The new tissue can always be 

 distinguished from the old because it is unpigmented. 



In Thyone briareus, the intestine begins to regenerate as soon as the 



