SITUS INVERSUS IN ECHINOIDS 



111 



aware, the similar cases among Echinoid larvae have only been 

 recorded twice by Eunnstrom. He described two such 

 larvae of S t r o n g y 1 o c e n t r o t ii s 1 i v i d u s reared at Monaco. 



Text-fig. 2. 



mv 



pc 



Transverse sections of an eleven-day -old reversed larva of Echinus 

 m i 1 i a r i s . x 300. 



am, amniotic invagination ; ax, axial sinus ; dp, dorsal pore ; 

 ep, ciliary epaulette ; g, stomach ; hy, hydrocoele ; in, intes- 

 tine ; mv, madreporic vesicle ; oe, oesophagus ; pc, pore-canal ; 

 rpc, right posterior coelom ; st, stone-canal. 



[Case A.] Eunnstrom, 1912 (23), pp. 2-3, 'no. 1'; 

 1918 (36), pp. 419-20. 



Left : no hydrocoele developed, but instead of it a ventral 

 primary pedicellaria was formed. 



