246 ^'- J- Crozier, 



dition of the whole organism, and that it is not absolutely dependent 

 on the presence of the nerve ring. The fact that intact individuals 

 were more successful is explicable on the basis of a great loss of 

 muscular tone suffered by mutilation. The rôle of the so-called 

 central nervous system in autotomy as seen in various holothurians 

 is analogous to that which this organ plays in the regeneration of 

 diverse forms — in some (Synapta) it constitutes part of a necessary 

 complex, while in others (Holothuria, and possibly Thyone) it does not. 



g) Regeneration. 



a) In nature. Approximately ten percent of the animals 

 observed {H. surinamensis only) were found to have anterior or 

 posterior ends much lighter in color than the rest of the body. 

 Posterior ends of this type were more frequently encountered than 

 anterior ends — twenty of the former and twelve of the latter 

 being noted among three hundred specimens. No case was observed 

 in which both anterior and posterior ends were of this kind. The 

 size of the parts referred to is seen in Table I. Such terminal 

 regions were readily recognized by their pale yellow pigmentation, 

 less than normal diameter, and (especially in the case of the 

 posterior ends) their low degree of contractility when stimulated. 

 Tentacles on these ends were thin, short and very slightly pigmented. 

 The possibility suggested itself that these lightly colored parts are 

 formed by regeneration, subsequent either to autotomous bisection, 

 or to injury by such enemies as fishes and the lai'ge blue crabs 

 {Callinectes) which abound in localities where H. surinamensis was 

 found. The latter explanation seems improbable, for the integument 

 of Holothuria, though relatively thin, is very tough and not easily 

 cut. There is no evidence that Holothuria has enemies of this kind. 

 Moreover, the fact that other holothurians (Daltell, 1851; Vol. I, 

 p. 74 et seq., tab. 14; and later workers) are known to show self- 

 divison, coupled with the remarkable powers of regeneration ex- 

 hibited by other genera, makes the first suggestion the more pro- 

 bable. ToEELLE (1909) found that mutilated fragments of the Aspi- 

 dochirota studied in her experiments (including three species of 

 Holothuria) were extremely tenacious of live, but did not readily 

 regenerate. Experiments shortly to be discussed showed that an- 

 terior and posterior ends exactly similar to those observed under 

 natural conditions were formed in a short time after the removal 

 of the appropriate part. While I have not seen a case in which 

 self-division was in progress, it is nevertheless entirely possible 



