AUTOTOMY IN HOlLOTHURIANS. 47 



nation of conditions causes the inner branches of the longitudinal 

 muscles to be broken. 



V. General Considerations. 



It is apparent from the experiments which have been described 

 that autotomy is not the result of any single factor which can be 

 easily controlled, at least in the two species of holothurians 

 studied. It is of more uniform occurrence in Leptosynapta than 

 in Thyone, a fact doubtless due largely to the structural differ- 

 ences between them. Clark ( :oi, p. 25) in speaking of Lepto- 

 synapta says, " Autotomy is not normal or defensive, but is due 

 entirely to pathological conditions." Some holothurians [e. g., 

 Cucuinarid), however, are said to multiply regularly by constrict- 

 ing the body in two in the middle (Lang, '96). Self-mutilation 

 probably occurs in nature as a result of such conditions as foul 

 water or two high temperature. The process might be beneficial 

 to either of the two species under consideration when the environ- 

 mental conditions were unfavorable for existence. By throwing 

 off a portion' of the body the total amount of metabolism neces- 

 sary would be decreased. An individual might thus survive 

 until conditions were again favorable and the lost parts could then 

 be regenerated. 



It can be affirmed that autotomy is apt to occur as a result of 

 unfavorable stimulation in both Leptosynapta and Thyone. In 

 the former genus it is induced uniformly and regularly when the 

 proper conditions arise, e. g., lack of sand for burrowing, foul 

 water. It might in this case be considered to be a definite reflex 

 and evidence has been given (II., p. 43) which lends some 

 support to such a view. The fact that the constrictions which 

 pinch the body in two are formed only when a region is connected 

 with the anterior portion of an animal shows that some influence 

 which comes from the anterior end is essential. It seems reason- 

 able to suppose that such an influence comes from the only 

 central nervous system which holothurians possess — the nerve 

 ring. Autotomy apparently involves a reflex in this case which 

 is similar to those found in arthropods (Drzewina, : 07 ; Morgan, 

 :02; Torre Bueno, : 08). 



When we turn to Thyone, however, autotomy is by no means 



