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THE AMERICAN NATURALIST [Vol. XL VIII 



part of itself to appease the hunger of its enemy lacks 

 confirmation, since the viscera are distasteful to fishes 

 and to some other animals. It may be that the autotom- 

 ous elimination of the Cuvierian organs serves a defen- 

 sive purpose, as pointed out by Ludwig and Minchin, and 

 Minchin suggests that the viscera may also be lost in this 

 process and thus incidentally be associated with a pro- 

 tective response. In the case of Thyone, however, evis- 

 ceration can hardly be considered defensive, and certainly 

 it is not a process of self-division for only one part pro- 

 duces a new individual. Clark ( '99) in discussing self- 

 mutilation in the synaptas states the matter clearly in 

 the following terms : 



I agree entirely with Cuenot ('91) in believing that autotomy is not 



never saw a ease of it in synaptas supplied with plenty of sand and an 

 abundance of sea water. 



Lang ( '96) points out one of these pathological condi- 

 tions, and recounts the fact that 



A Stichopns was observed to come entirely out of its skin, i. e., the 

 whole integument dissolved into slime, so that only the dermo-museular 



In the present paper I have mentioned that Thyone at 

 times appears to undergo a similar softening of the 

 tissues in the region where the break occurs, and Pearse 

 ('09) showed that autotomy is due, at least in part, to a 

 structural arrangement which he considers is accidental 

 in character. My observations further show that local 

 constrictions undoubtedly have an important part in sepa- 

 rating the retractors from the radial longitudinal muscles. 

 All of these factors are pathological and are due to exter- 

 nal or internal stimuli. The external (extra-cellular) 

 stimuli, mechanical and chemical, as tried by Pearse 

 ('08), appear to be less effective in producing autotomy 

 than the purely internal (intracellular) stimuli such as 

 lack of oxygen and its associated phenomena. The chem- 

 ical (strychnine) that produced the largest percentage 

 of evisceration in Pearse 's experiments, probably affected 

 respiration, since it greatly increased the activity of the 



