21 



oral to aboral end, new tissue formed along the cut edges so that the 

 Avound healed comiDletely. 



Among the individuals cut into two transversely, then slit longi- 

 tudinally and all organs removed, one posterior piece, containing the 

 cloaca, healed along the cut edges in two directions, and a new intestine 

 had regenerated when it was killed, June 8 th, 128 days after the 

 operation. 



Two out of five individuals in which 2 cm of the length of a radius 

 was removed regenerated the lost part ; while four out of five of those 

 in which 2 cm of the length of the inter-radius was removed, completed 

 themselves. 



In the animals in which a transverse cut was made across one 

 radius and one inter-radius, all regenerated the missing part. 



In the animals in which the body-wall was removed anterior to the 

 lantern, but no tentacles or other organs injured, all regenerated the 

 part removed. 



In connection with the above account of Ti)yone briareus and Cucii- 

 maria grubi it may be of interest to note that apparently Cucuiiiaria 

 plaiicl regenerates with equal facility, both anterior and posterior parts 

 of the body. But in all other Dendrochirota observed, the operation most 

 favorable to the regeneration of the animal is the one which consists in 

 dividing it transversely just posterior to the lantern. After such an 

 operation, most of the posterior parts complete themselves, but except 

 in the instances cited for Cucumaria grubi., no anterior parts regenerate. 

 It is not at this time advisable to attempt an explanation of the appar- 

 ent inability of anterior parts to regenerate; but the most important 

 factor in the regeneration of the Holothuria seems to be the presence of 

 the cloaca through which respiration principally takes place in the 

 normal individual. This is indicated by the fact that all parts of animals 

 of whatever size, lived four months or more if the part contained the 

 cloaca; but twelve out of fifteen individuals in which only the cloaca 

 was removed, died ,, within" a comparatively short time. Individuals 

 belonging to the two species Cucumaria grubi and Cucumaria planci 

 were the only ones who survived the removal of the cloaca. 



Among the Synaptidae , no part of the body less than five cm in 

 length and deprived of the lantern and tentacles survived longer than 

 three days. 



The Aspidochirota are extremely tenacious of life, the empty body- 

 wall of one-half to one-third of an animal may live two months or more 

 and possesses, the power of movement to an extradinary degree; but 

 regeneration does not readily take place in any of the species observed. 



