270 



Prof. E. W. MacBride. 



FIG. 2. Diagrammatic Longitudinal Frontal Section of a Larva about 18 days old. 



ad., ce., st., stom., as before ; EcJi., invaginated ectoderm about to form the oral 

 disc of the future Echinus ; hy., hydroccele ; l.a.c., left anterior coelom (ampulla of 

 stone-canal) ; l.p.c., left posterior coelom ; m.v., madreporic vesicle (right hydro- 

 ccele this is not in the plane of the figure) ; r.a.c., right anterior coelom ; 

 r.p.c., right posterior coelom. 



st.c. 



FIG-. 3. Diagrammatic Transverse Section of a Larva about 18 days"old. 



Names as before ; in addition, int., intestine; m.p., primary madreporic pore; 



p.c., pore canal. 



