174 



Mr. H. Ohshima. Reversal of 



case, as maintained by Grave ((4), p. 45), can easily be overcome, because the 

 development of the double liydrocoele is not a feature of adaptation to larval 

 life, as he assumes it to be. 



The unusual development of a hydrocoele on the right side when the left 

 hydrocoele is arrested in its development resembles the well-knov?n pheno- 

 menon in the regenerating claw of Alpheus (Przibrara (8)). If the large claw 

 of this crustacean is amputated, this will be replaced by a small claw, whilst 

 the small claw on the other side, which has not been operated upon, will 

 become a large claw. Przibram called this " compensatory hypertypy." 

 Obviously these two cases are different in that (i), whereas in the Echino- 

 pluteus there is no trace of a right hydrocoele in normal condition, the small 

 claw of Alpheus represents neither a rudimentary condition nor an early 

 developmental stage, but is quite a functional organ ; and that (ii), whereas 

 the left hydrocoele of the Echinopluteus is arrested in its development during 

 its very early stage, the large claw of Al23heus is removed after it has fully 

 developed. With the sense widened to include these two cases, Przibram's 

 term is desirable to be adopted here also. 



The manner in which the situs inversus occurs in Echinoplutei resembles 

 that found in the Triton larvse, as produced artificially by Spemann ((15), 

 p. 407). In both cases the abnormality starts with a " defective " develop- 

 ment of a single organ — the gut in Triton and the hydrocoele in Echinus. 

 There is, however, a difference between the two in the further courses in 

 which other organs are affected. In Triton the other adjoining organs are 

 simply displaced by that abnormal behaviour of the gut, while in JSchimis a 

 new hydrocoele appears on the right side, and a new set of calcareous 

 structures, etc., are thereby induced to develop. The left hydrocoele can, if 

 it regains its chance of further development, produce another echinus- 

 rudiment, so as to give rise to a double-hydrocoele larva. Such a feature is 

 very improbable to occur in the case of Triton. 



My interpretation of the double-hydrocoele formation as described above 

 cannot hold true in the case of starfish larvse. Usually in the starfish larva 

 the coelomic vesicles on both sides fuse and communicate with each other at 

 the anterior end, and the right dorsal pore, if present at first, gradually 

 atrophies. Here in this case the obliteration of a dorsal pore has no influence 

 upon the development and differentiation of the hydrocoele on the corres- 

 ponding side. Under such different conditions I think that the occurrence 

 among starfish larvse of the situs inversus as is found in Echinoid larvse will 

 be extremely uncommon. Gemmill's interpretation as to the cause of the 

 double-hydrocoele formation ((3), pp. 54-55) cannot, in its turn, hold true in 

 the cases of the Echinoid and Ophiuroid larvse, as was pointed out by 



