THE VISCERAL MASS IN ANTEDON ROSACEUS. 311 



first formed simply from the open end of the gut diverticulum which 

 extends into the arm. 



The non-occurrence of this phenomenon in Ophiuroids appears to 

 me to be due to the absence of any gut diverticula in the arms of the 

 latter, so that a separated arm is entirely without any portion of the 

 alimentary canal, by the growth of which the remainder can be regene- 

 rated. Schizogony, however, occurs in both Asteroids and Ophiuroids, 

 probably because, in this case, the disc itself divides into two parts 

 and hence each of the resulting halves will contain a portion of the 

 alimentary canal, whether or not the latter be produced into the arms. 



It thus appears that regeneration, so far as it is known, in Asteroids 

 and Ophiuroids is very different from that which takes place in An- 

 tedon, for, in the two former groups regeneration never appears to 

 occur when the alimentary canal has been entirely removed. 



Unfortunately Professor Haeckel has only been able to examine the 

 external characters of the comet forms described by him; further 

 research will probably throw much light on the subject, and, if comet 

 forms should ever be found to occur in Ophiuroids, it may be possible 

 to institute a closer comparison in respect of regeneration between 

 Antedon and Ophiuroids than between Antedon and Asteroids. 



On the regeneration of lost individual arms in Asteroids and Ophiu- 

 roids it is needless to dwell; this phenomenon finds a parallel in the 

 regeneration of the arms of Antedon. 



As yet little is known concerning the ejection and regeneration of 

 the viscera, including the alimentary canal, in Holothurians, beyond 

 the mere fact that it does occur, and this was shown to be the case by 

 Daly ell. 1 It is possible that we have here a more exact parallel to 

 what takes place in Antedon than in Asteroids or Ophiuroids. 



I have stated above that the meaning of the process in Antedon, 

 supposing it to be a normal occurrence, must for the present remain 

 undecided; suffice it here to offer, as a suggestion, the only explanation 

 which seems at all probable. Crinoids, unlike most Echinoderms, have 

 no selective power over their food supply ; all sorts of food, good or 

 bad, wholesome or poisonous, are carried into the alimentary canal by 

 the action of the cilia in the ambulacral grooves. If any irritating or 

 poisonous particles, or even any dangerous parasite, were conveyed by 



1 The Powers of the Creator, displayed in the Creation, London, 1851, vol. i., p. 49 et seq. 

 It was only after considerable difficulty that I obtained this reference, for which I am 

 indebted to Professor F. J. Bell, who also pointed out to me Semper's remarks on the 

 subject; Reisen in Archipel der Philippinen, vol. i., Holothurien, p. 200 et seq. 



