138 HIROfHI OHSHIMA 



stated there is a group of pointed spines and a solitary one on 

 each side of the larva. Runnstrom found such a spine 

 only on the left side (Case 26). I am much inclined to think 

 that from want of regulating influence of the hydrocoele the 

 rudiments of podicellariae were developed in an aberrant 

 way into some of those peculiar spines. 



Runnstrom (27, pp. 21-2, figs. 21-3) discovered in the 

 normal larva of Echinus miliaris a pair of small ecto- 

 dermal invaginations formed inside the loop of the ciliary 

 band on the right side. In each of these invaginations 2-3 

 spines belong to the Basalia 3 and 5 are later formed. He called 

 the former ' spine invaginations ' (26, p. 420). Spines un- 

 doubtedly identical with these have been seen by me on the 

 left side of one of the reversed larvae (Text-fig. 1, spj. In 

 Strongylocentrotus livid us these structures do not 

 appear normally, still Runnstrom identified the pair of 

 pits found in an abnormal larva with them (Case B). These 

 may be an abnormal amniotic invagination divided into 

 two. His descriptions and figures (23, p. 8; 26, pp. 420-1, 

 Taf. xiv, fig. 13) are not quite satisfactory enough to sub- 

 stantiate his refusal to look on them as modified amniotic 

 invaginations. 



(j) Gut . — We know really nothing about the change the 

 gut undergoes in accordance with the formation of the double 

 echinus-rudiment or situs inversus. Normally the definitive 

 stomodaeum appears at the centre of the floor of the epineural 

 space (MacBride, 11, p. 307), and the rudiment of the 

 oesophagus, as an outgrowth from the left wall of the stomach 

 meeting the stomodaeum, appears later (p. 310). The adult 

 mouth breaks through some days after metamorphosis, and the 

 anus is formed still later (pp. 311-12). Runnstrom (24, 

 pp. 544-52) found in the larvae developed from the eggs which 

 had been treated with potassium-free sea-water some asym- 

 metrical distortions in the larval stomach and formation of 

 a new oesophagus on the left. He interpreted the phenomenon 

 as the formation of the definitive oesophagus precociously 

 indicated. It is quite conceivable that in the course of the 



