SITUS INVERSUS IN ECHINOIDS 12-5 



There was only a single dorsal pore, and no trace of madreporic 

 vesicle was found. 



[Case 15.] Echinus esculentus. MacBride, 1911 

 (14), pp. 241-4, PL xxiv, figs. 2-4. Reared at Plymouth 

 (de Morgan). 



Echinus-rudiments fully developed when examined and 

 drawn by the observer, the larva then being fifty-five days old. 

 The echinus-rudiment of the right side- very slightly smaller 

 and less advanced, than the left one. Two pedicellariae 

 developed on the right side and a third appeared at the 

 posterior end. 



[Case 16.] Strongylocentrotus livid us. v.Ubisch, 

 1913 (30), pp. 440-3, Text-fig. t, Taf. viii, fig. 26. Reared at 

 Naples (Giesbrecht). 



Axial sinus well developed on both sides and almost the same 

 in size, each beset with a pore-canal, which opened to the 

 exterior separately by dorsal pores. Mid-dorsally-situated 

 madreporic vesicle communicated through a narrow canal 

 with the right axial sinus. Echinus-rudiments and stone- 

 canals on both sides equally well developed. 



[Case 17.] Echinus miliaris. MacBride, 1918 (15), 

 pp. 338, 347, PI. V, fig. 8. Reared in London. 



Echinus-rudiments on both sides of almost equal size. 

 Dorsal pores two, and no pedicellariae. 



[Case 18.] Echinus miliaris. MacBride, 1918(15), 

 pp. 339, 347, PI. vi, fig. 10. Reared in London. 



Both echinus-rudiments nearly equal in size, the right one 

 slightly smaller. Dorsal pore single. A single pedicellaria 

 formed on the right side. 



[Case 19.] Echinus miliaris. Culture 1, ' control '. 



The larva when found was eighteen days old, and had a lobed 

 hydrocoele, stone-canal, and amniotic invagination developed 

 almost exactly in the same state on each side. Two pore-canals 

 opened separately through a respective dorsal pore. The larva 

 has been carefully fed on sufficient food, and the echinus- 

 rudiments on both sides developed at equal rate. The two 

 dorsal pores retained as before their side-by-side positions. 



K 2 , 



