128 THE BIOLOGY OF THE SEA-SHORE 



regeneration. Normally, the left respiratory tree, the upper 

 part of the gullet and the genital organs are retained in the 

 body cavity, but on occasion the whole of the viscera may be 

 thrown off. Semper (quoted by Ludwig, 1889-92) records 

 that a specimen of Holothuria scabra, which had thrown off its 

 gut close behind the ring-canal and the left respiratory tree 

 and genital organs along with it, had regenerated everything 

 except the genital organs in nine days. The power of 

 regeneration has also been found to extend to the calcareous 

 ring and to the tentacles. 



Stimuli of a more or less similar nature to those which 

 cause self-evisceration in many Holothurians give rise in the 

 Synaptids to a process of self-division. Contraction of the 

 circular muscles of the body wall causes the body to constrict 

 at one or more places, and to fall into pieces. Some species 

 are said to be so sensitive as to break up at the least approach 

 to rough handling, and are, in consequence, very difficult 

 to collect and keep. Here, as in several other instances we 

 have noticed, the nature of the phenomenon has not been 

 satisfactorily explained. Quatrefages (1842), one of the 

 earhest observers, tended to regard it as a normal mode of 

 reproduction capable of occurring spontaneously. On the 

 other hand, it is generally agreed with regard to this process 

 in Synaptids that it is only the head portions which regenerate 

 new individuals. Semon (1887) has noticed that the autotomy, 

 if we may so call it, occurs at the point where the body is 

 gripped by the collector, the head end then burrowing 

 quickly into the sand. He consequently regards it as a 

 means of escape from enemies, the animal saving its life by 

 the sacrifice of a portion of its body. Ludwig {op. cit.) tends 

 to the opinion that self-division in Synaptids is more or 

 less of a pathological response to unaccustomed conditions. 

 This view draws support from the fact that in Quatrefages* 

 experiments the self-division occurred more frequently as 

 the period of confinement in the aquarium grew longer. 

 Ludwig further points out that the restriction of this 

 habit to the family of the Synaptids need cause no 

 wonder, since they alone among Holothurians possess a 



