48 A. S. PEAHSE. 



SO uniform and regular in its occurrence. Under the best of con- 

 ditions it appears in only 35 per cent, of the possible cases. As 

 has been stated, the phenomenon depends in this genus upon the 

 breaking of certain muscles and the rupture of the body-wall. 

 In some individuals there seems to be an actual struggle between 

 the different parts of the body, and the observer is often in doubt 

 for a time whether the longitudinal muscles will pull the visceral 

 organs back within the body or whether the intense contraction 

 of the general body muscles will eject them. One is easily led 

 to believe that the activities of different parts are not well corre- 

 lated, and that the part which gets the initial advantage gains 

 control. 



As the mechanism for ridding the body of certain parts is quite 

 different in the two genera under consideration, it is not possible 

 to compare them directly. The process is more stereotyped in 

 Leptosynapta. In the opinion of the writer, the words which 

 were just quoted (p. 47) from Clark (: 01) in regard to that genus 

 could better be applied to Thyone and it seems improbable that 

 autotomy is an important factor in the daily life of the members 

 of either genus. Nevertheless, it is easy to conceive that a proc- 

 ess of this kind, which first arose as a result of certain struc- 

 tural and physiological peculiarities, might in time give rise to a 

 process which would become advantageous to the species. In 

 fact, this condition of affairs seems to have come about in some 

 holothurians {e. g., Cuciunarid) which multiply by constricting 

 the body in two in the middle. 



The tendency toward autotomy is apparently marked in the 

 holothurian line. It is a phenomenon which is accompanied by 

 remarkable powers of regeneration and in some species it has 

 become a beneficial process, but in others it is comparatively un- 

 important, if not actually harmful. 



VI. Summary. 



I. In Leptosynapta inhczrens autotomy occurs regularly when 

 unfavorable conditions of environment arise. Experiments with 

 Thyone briareus did not show more than 3 5 per cent, of cases of 

 autotomy, even under the most favorable circumstances for its 

 occurrence. 



