149 



we might have to do here only with abnormal larvae is quite inacceptable ; 

 it would be impossible for a larva with such incomplete digestive organs, 

 and accordingly unable to feed, to form the long postoral arms and the 

 whole body skeleton in a perfectly normal way. (That the transverse rods 

 are somewhat different from those of the fully formed larvae is evidently 

 due to the absorption during metamorphosis). This, however, leads to an- 

 other important problem. It is evident that the considerable growth of 

 the regenerating larval body could not take place without some food sup- 

 ply. The "larva" itself being unable to feed until the new digestive organs 

 are ready to function, there must be some nourishment stored somewhere. 

 This also appears to be the case. In the vibratile band of the posterolateral 

 arms there is generally seen a great number of very fine refractile grains. 

 These might well represent the food supply; in fact, it is hard to see, 

 where it could otherwise be found. 



Of course, I do not mean to maintain that definite proof of this astonish- 

 ing regeneration has been given. But the available material certainly in- 

 dicates that it does take place. The problem most urgently invites closer 

 investigation. 



The fact that this larval type is found both in the West Indies and in 

 the Indian Ocean gives a valuable hint as to the question to which Ophi- 

 urid type it belongs. Still it is not sufficient for solving the problem, and 

 an attempt to find out the parental forms on the base of our present know- 

 ledge would be essentially guess work of very doubtful value. 



Ophiopluteus sitnilis Mitsn. 



PL XXVII, Fig. 3. 

 Th. Mortensen. Die Echinodermen-Larven d. Plankton Exped. p. 60. Tat'. V. 8; VI. 4. 



The specimen figured, which was taken at Misaki, Japan, 29/VI. 1914, 

 I am unable to distinguish by any notiqeable character from the 0. similis 

 from of! the Cape of Good Hope described in the work quoted. The more 

 upright position of the posterolateral arms is hardly a reUable character 

 but probably due to preservation, as, in fact, the arms of many Ophiurid 

 larvae are apt to bend and curve when the larvae are mounted in Canada- 

 balsam, especially such forms as have long arms with slender supporting 

 rods. (In the present specimen all the arms are much curved, but have 

 been restored to their natural shape in the figure). There is a distinct sub- 

 oral cavity. 



The skeleton (Figs. 77, 78) presents some minor differences in the shape 

 of the transverse rods, which may perhaps indicate that the specimen from 



