sure that it exists in the adult ophiuran. 



MgBRIDE (9) and GOTO (5))both agree that in 

 star-fishes the inner perihaemal ring sinus arises 

 from the anterior enterocoele although they differ 

 as to the method of its formation. In none of the fawn, 

 I hav-? is the structure ih question fully formed 

 but in stage "F" a cavity is originating f as an out- 

 grov/th from the anterior enterocoele in the stone 

 canal interradius:, which I take to be the rudiment 

 of the inner perihaemal ring space. It lies to the 

 left of the -tone canal near the median sagittal 

 plan: of the larva. From the posterior silo of the 

 ventral end of the anterior enterocoele the outgrowth 

 takes its origin, then extending posteriorly until 

 past the water ring, it bends over and grows down 

 until its end reaches the nerve rine; at a point in- 

 side the outer perihaemal sinus. Here the end of the 

 pouch in question begins to spread under the nerve 

 rin~ in both directions, parallel to the outer peri- 

 haemal ring.Figs, 24 and 2S . ips. This coincides ex- 

 actly v.'it' its method of origin in Asterina gibbosa 

 as described by MeBRIDE. 



Although the outer perihaemal ring is entir 



