108 HIROSHI OHSHIMA 



and lying near the hind end of the body. Both the ventral 

 and dorsal opaiilottos were already separated from the ciliary 

 bands, the anterior transverse part of the latter showing a 

 peculiar twist which indicated the future position of the paired 

 pre- oral arms. 



A hydrocoele, stone-canal, and amniotic invagination were 

 all situated on the right side, whilst no such organs 

 were found on the left side. No special attention was paid 

 to such a slight asymmetrical distortion in shape of the stomach 

 as was often noticed by llunnstrom in some abnormal 

 larvae (24, 25). 



Similar larvae were found later to be fairly numerous, and 

 were transferred to a separate jar where they were allowed to 

 develop further. There was found no difference in the rate 

 of growth between normal larvae and these abnormal ones. 

 When fully grown (Text-fig. 1) the abnormal larva possessed 

 four pairs of well-developed arms, a large echinus-rudiment {rd) 

 on the right side, from which five primary tentacles often pro- 

 truded and moved actively. Whether a pair of pedicellariae 

 really appeared on the left side as is the case with Strongylo- 

 centrotus (see p. 130) I cannot assert at present, though it 

 seems to me to be highly probable. As to those paired cal- 

 careous structures which appeared on the left side, as seen 

 in the text-figure (sp^), I am almost certain that they were 

 groups of spines.^ The unpaired spine which should appear 

 in normal cases at the hind end, a little to the right of the 

 median line, was here found shifted to the left side (sp^). 



No less than half a dozen of such abnormal larvae passed 

 metamorphosis when a month old. As to the external feature 

 of these young sea-urchins one can find no difference from 



1 While dealing with the living larvae I thought without the slightest 

 doubt that the paired calcareous structures alwaj^s found on the left 

 side were really pedicellariae. Text-fig. 1. which is the only drawing 

 made of this stage from life and the only evidence now available, shows 

 that they are situated inside the loop of the ciliary band. This position 

 coincides precisely with that of the groups of spines as described by 

 Runnstrcim (27, pp. 21-2. figs. 21-3). In this particular specimen 

 at least there were present no true pedicellariae (see p. 138). 



