SITUS INVERSUS IN ECHINOIDS 121 



Bight : anterior coelom smaller than that of the left side. 

 A vesicle was seen to be produced from it, which latter the author 

 interpreted with some doubt as the hydrocoele. All these 

 parts were seen beginning to degenerate. Amniotic invagina- 

 tion formed very late, but soon disappeared. Pedicellariae 

 not formed. The posterior coelom produced an anterior 

 diverticulum, probably representing the genital stolon. 



[Case 3.] Strongylocentrotus lividus. v. Ubisch, 

 1913 (30), pp. 440-3, Text-fig. u. Eeared at Naples (Gies- 

 brecht). 



Left : axial sinus well developed with the pore-canal which 

 opened externally by a dorsal pore. Madreporic vesicle 

 (* dorsal sac ') large, lying close to the axial sinus, but no com- 

 munication between them existing at all. Echinus-rudiment 

 fairly advanced. Genital stolon developed. 



Right : axial sinus smaller than that of the left side, 

 pore-canal only represented by a knob from wall of the 

 former, and a fibrous tissue connecting the epidermis with 

 this knob. Echinus-rudiment less advanced than that of the 

 left side. 



[Case 4.] Strongylocentrotus lividus. Runn- 

 strom, 1918 (26), pp. 418-19, Taf. xiii, figs. 9, 10. Reared 

 at Monaco. 



Left : axial sinus, stone-canal, and hydrocoele all developed 

 normally. Pore-canal and dorsal pore present, the latter later 

 shifted its position towards the median line. Amniotic in- 

 vagination formed. 



Right : axial sinus well developed, with pore-canal and dorsal 

 pore. The latter hke its left fellow changed its position later 

 towards the median hne. Stone-canal formed later, its slight 

 expanded posterior end representing the hydrocoele. No 

 amniotic invagination formed. 



[Case 5.] Echinus miliaris. MacBride, 1918 (15), 

 p. 347, PI. V, fig. 9. Reared in London. 



Left : axial sinus fused with that of the right side and com- 

 municated with the exterior 'through a single pore-canal. 

 Echinus-rudiment large. 



