MONOGRAPH OF THK KXISTING t'KIXOlDS. 415 



The rejienerative powers of the disk are summarized by Przlbrara as follows: 



Eegeneration of an anal tube cut away proceeds regularly and the functioning 

 of the new anus can be observed after one month. Eegenerative power, therefore, 

 is not lacking in the disk, and its incapacity when detached to exist or to regenenvte 

 may be ascribed to the absence of sufficient ectodermal parts, and especially to the 

 absence of a sufficiently large portion of the ectodermal nervous system. 



A disk half detached grows again entirely onto the calyx. 



The following methods are employed to hinder the immediate return of the 

 disk to its original position : The detached half was cut away ; the calyx lining 

 under tlie loosened half was removed ; a strip of gummed paper was inserted under 

 the loosened half; and the oral pinnules, in the normal condition held above the 

 disk, were inserted under the detached portion. 



In the two last cases the dislcs were cast off; in the first two they grew com- 

 pletely on again, and since subsequently the disk were not always orientated accord- 

 ing to the orientation of the arms, it is to be assumed that the disks themselves 

 have assisted the regeneration to a certain degree. 



Disks can be transplanted from one animal to another if the original orienta- 

 tion is preserved. If not ca.st off the disks gi-ow fast in their new position in about 

 a week. 



Transplantation of the disk has no effect upon the color of regenerating arm 

 tips, which remain of the same color as before the disks were exchanged. In these 

 experiments caution is necessary, for regenerating arm tips of a yellow specimen 

 are sometimes red, and in the case of transplantation of the disk it would be easy 

 to ascribe this to the influence of a new red disk. 



Eeichensperger carried out experiments along the same lines. He cut off 

 the arms of five specimens at the radials without injuring the latter. In all cases 

 the disk was immediately thrown off. After four months two of the specimens 

 had regenerated five arms, from 1.1 mm. to 1.3 mm. in length; the other three were 

 dead. If during the amputation the radials are injured no regeneration wiU occur. 



When the central capsule of armless specimens was injured with a fine pin no 

 regeneration took place; but in two of the three specimens in which four or five 

 brachials were preserved regeneration set in in spite of the injury to the cen- 

 tral organ. 



If after the removal of the arms the dorsal cord in the radials be injured, re- 

 generation never occurs, even if the IBr^ be preserved. 



Eeichensperger believes that his investigations appear to confirm the existence 

 of a regenerative zone at the base of the arms, and concludes that a certain mini- 

 mum of the substance of the dorsal nervous system, and especially of the wandering 

 cells, must be present uninjured to give rise to regeneration. 



Eeichensperger found that single arms would regenerate nothing, and that 

 arm pairs regenerated only if attached to a part of the calyx which contains a 

 fragment of the central organ; but in the latter case if the distal brachials be 

 removed or the arms otherwise injured no regeneration occurs. 



In the arms regeneration takes place with equal facility at all points, on the 

 distal end of any brachial, or on any fractured surface within the substance of any 



