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THE AMEBIC AN NATURALIST [Vol. XLVIII 



depended entirely upon an accidental structural defect. 

 Another thing noticed is of interest in this connection. 

 When splitting open the body wall of an animal that was 

 eviscerating, and thus relieving any internal pressure that 

 might be due to contraction of the circular muscles, some 

 of the retractors were seen still attached to the longitu- 

 dinal muscles. Under these conditions it would not be 

 possible for the retractors to exert any pull against the 

 pressure produced by the circular muscles, yet the re- 

 tractors were observed to constrict off or break away 

 from the longitudinal muscles by what appeared to be 

 purely a local disturbance. It is hard to see how this 

 could happen, or how the skin continues to separate 

 around the calcareous ring after the first break is made, 

 if the process of evisceration depends solely upon the 

 breaking of retractors and internal pressure. Indeed, 

 the view that local changes take place in the tissues is 

 supported by other facts. Leptosynapta, if left in stag- 

 nant water or under other favorable conditions, under- 

 goes repeated autotomous fission as the result of local 

 constrictions, and Pearse states that autotomy depends 

 upon the presence of the anterior portion of the body, 

 and presumably upon the presence of the circumoral 

 nerve ring. However, he found in Thyone that highly 

 irritating substances like acetic acid and clove oil did not 

 produce ejection of the viscera. 



mm. i! - autotomy. The same may be said of sodium chloride, atropine 

 and clove oil, although the injection of any of these substances was 

 often followed by a waving of the oral tentacles to perform feeding 



These results would indicate that the nervous system 

 is not primarily involved. Certainly the ejection of vis- 

 cera may occur in Thyone without any visible external 

 stimulus. 



The parts eviscerated in Thyone have already been 



