AUTOTOMY AND REGENERATION 125 



a strong argument in favour of the adaptive nature of the 

 autotomy. Against such an interpretation, however, Morgan 

 places the fact recorded by King that " ahhough the arm 

 regenerates faster at the base, yet a new arm is not any 

 sooner produced in this way, since there is more to be pro- 

 duced, and the new arm from the base may never catch up 

 to one growing less rapidly from a more distal cut-surface, 

 but having a nearer goal to reach." 



The name " brittle-star " accurately describes the marked 

 tendency, well known to shore collectors, which members of 

 this group have towards autotomy. When removed from a 

 rock pool to the palm of the hand a brittle-star will fre- 

 quently autotomise its arms, piece by piece, until practically 

 nothing but the disc remains. Preyer (quoted by Ludwig, 

 1 901) finds that autotomy occurs, as a result of various kinds of 

 slight stimuli, particularly readily in the six-rayed or seven- 

 rayed Ophioactis virens, and also in Ophioderma, Ophiomyxa, 

 and Ophioglypha. Either the arm is shed in one piece — at 

 a level above the point of application of the stimulus — or it 

 at once breaks up further into several pieces, the latter being 

 the more usual method when the autotomy takes place out 

 of water. 



Regeneration is said to take place at any region, and the 

 same observations as in starfishes have been made on the 

 rate of regrowth of the arm at different levels ; in other words, 

 the closer to the disc the arm is severed the more rapidly it 

 regenerates. This has been noted by Stockard (1908) for 

 Ophiocoma riisei and for another, undetermined, species of 

 Ophiuroid. Another writer, Morgulis (1909), has some 

 interesting observations on the effect, upon regeneration, of 

 injury to the radial nerve prior to amputation of the 

 arm. He finds that if, in Ophiocoma pumila, the radial 

 nerve is injured in advance only a small stump is regenerated. 

 Similarly, if the nerve is destroyed close to the disc so little 

 new tissue is formed that it is difficult to recognise it at all. 

 When the radial nerve is left intact a long new part is re- 

 generated. In cases where the brittle-star throws off the 

 arm at the place of injury to the nerve, there is absolutely no 



