74 S. HIROTA. 



noch keine Spur von Eegeneration zeigten ; sehr wahrscheinlicli wareii das 

 solclie, die kurz iiach dera Einfangen sich abgelost batten." This stands also 

 in favor of a view that the breaking is accomplished comparatively quickly. 

 Sometimes, we find parasitic Gasteropods* — SHlifer Unchiae and TJtyca 

 ectochonca — inhabiting the integument, but it is certain that the}'' do not 

 assist in the breaking of arms. 



I have unfortunately no specimen of detached arms of Lincliia, but I 

 have two of OpJiid taster. In them the wall of the wound is entirely covered 

 by a membrane, over which calcareous pieces of various sizes are deposited.. 

 There is left a narrow smooth area near the ambulacral furrow, but there 

 exists yet no oj^ening comparal)le to a mouth. It is highly probable that a 

 similar state of things is shown in Linckia in the corresponding stage. 



From all the preceding statements we may be justified in the following 

 conclusions : 



I. In a typical ' comet ' the cefitral organs — the neuro-vascular system 

 being out of consideration — are developed as in a normal young, 

 having a disc of the same size. 

 II. The younger the ' comet ' the relatively greater in girth are the re- 

 generated a.rms. 



III. The first ambulacral plate and the stomach retractor muscles of the 

 principal arm are secondarily formed after the arm is dropped, so 

 that a radial symmetry in the disc is not much aifected through the 

 existence of the mateless arm. 



IV. The stone canals are formed on both sides of the base of the principal 

 arm and the madreporic plates from ordinary ossicles on the dorsal 

 edge of the former wound. 



V. A local constriction of an arm is not to be taken as the preparation of 

 self-breaking which takes place abruptly, but indicates a junction be- 

 tVk^een the original, and the regenerated parts of an arm. 

 YI. The breaking may be caused in any arm and at various positions, at 

 the will of the animal. 



* These are illustrated in P. and F. Sarasin's ' Ueber zwei parasitische Schnecken.' Ert^. 

 naturwiss. Forsch. auf Cevlon. 1. Bd. 1887-88. 



