No. 569] 



REGENERATION 



305 



and hence shows great variability in the different species 

 of holothurians, this does not in any way explain the 

 great excess of these vesicles on the left side of Thy one 

 briareus. In regeneration, probably through the influence 

 of functional correlation, there is a tendency for the old 

 tissue to reproduce the exact number and arrangement 

 of the lost vesicles, but it may reproduce a somewhat 

 more radial (ancestral) arrangement. 



Enough has been given in this paper to show the need 

 of a more extensive and intensive reexamination of the 

 Polian vesicles. This would give a better idea of their 

 morphological and functional significance. The follow- 

 ing summary and conclusions are based on the work 

 described : 



1. Evisceration in Thyone includes the following or- 

 gans: Esophagus, stomach, intestine, calcareous ring, 

 nerve ring, tentacles, ring canal, Polian vesicles, stone 

 canal with madreporite, and the retractor muscles of the 

 esophagus. 



2. The method used to produce evisceration was to 

 allow Thyone to stand in stagnant water until it became 

 foul. This was followed by treatment with running water 

 containing much oxygen. Alternating these processes 

 produced as high as 65 per cent, of self-mutilated indi- 

 viduals. 



3. The structural accident theory of Pearse is inade- 

 quate to explain all of the conditions arising in the proc- 

 ess of autotomy. At times the skin appears to dissolve 

 away with little or no pressure present, and retractors 

 frequently break off by local constrictions instead of by 

 longitudinal pull. 



4. The parts eviscerated are at first highly irritable, 

 and may be kept alive for some time. The part remain- 

 ing is less responsive, but reacts to touch, to lack of 

 oxygen, and probably to other stimuli. 



5. Regeneration of all lost organs may occur, but it 

 takes place only when all parts concerned in evisceration 

 are completely expelled. Otherwise the animal dies. 



