124 HIROSHI OIISHIMA 



a solid thickening at the dorsal end of the stone-canal, while 

 the latter also has no visiljle lumen (sf). Pore-canal repre- 

 sented ])y a solid cell-mass (pc'), Hydrocoele simple and 

 vesicular (%')• No amniotic invagination. 



Eight : anterior coelom well developed (ax), with its external 

 communication through a pore-canal (jpc) and dorsal pore {djp). 

 Madreporic vesicle with fairly distinct lumen (mv), with its 

 wall in contact with the axial sinus, but no communication 

 whatever existing between them. Htone-canal (st) formed 

 normally, and hydrocoele (hy) well developed, being provided 

 with five lobes. Amniotic invagination formed (am). 



I Case 11.] Echinus miliar is. Culture 9, 'treated'. 

 Tliis was also fifteen days old when found and killed. 



Left : no trace of axial sinus and pore-canal to be found. 

 Stone-canal ending ])lindly at the anterior end, while posteriorly 

 it opens to a small widened cavity of the hydrocoele. Amniotic 

 invagination formed but small. 



Eight : axial sinus, pore-canal, dorsal pore- and stone- 

 canal all well developed. Madreporic vesicle lying close to 

 the pore-canal. Hydrocoele lobed. Amniotic invagination 

 a little smaller than the left one. 



(c) The hydrocoele and its associated structures of both sides 

 equal in their state of development or nearly so. 



[Case 12.] Spatangoid pluteus collected at Messina. 

 Metschnikoff , 1884 (17), p. 64. 



Echinus-rudiments with ambulacral feet and spines * quite 

 equally ' developed on both sides. 



[Case 13.] Mellita pentapora. Grave, 1911 (9), 

 pp. 35-46, Text-figs. 1-3. Eeared at Beaufort, N.C. 



Axial sinuses, hydrocoeles, and amniotic invaginations of 

 both sides very nearly equal in development and symmetrically 

 arranged. Two pore-canals opened by a common dorsal pore 

 situated on the mid-dorsal line. 



[Case 14.] Echinus miliaris. MacBride, 1911 (14), 

 pp. 237-41, PI. xxiv, fig. 1. Eeared in London. 



Here also axial sinuses, hydrocoeles, and amniotic invagina- 

 tions were found almost exactly in the same state on both sides. 



