RELATION OF LARVA TO ADULT. 

 THe hydroeoel is the first organ tc show radial 

 symmetry in the developing larva of Ophlura brevispina 

 and from the time when this organ has completed its 



rotation about the oesophagus it shows a definite re- 

 lation to the plane of bilateral symmetry of the larva, 



. The hydrocoeleis not only radially symmetrical 

 but bilaterally symmetrical, since it is divided into 

 symmetrical halves by the plane which passes through 

 radial canal 3 .and through the interradius or the 

 stone canal. This plan: coincides with the plane of 

 bilateral symmetry of the larva. She ether parts of 

 the star are built about fche water v r system 



hence it as a whole bears a similar relation to the 



•tl 

 larvs as was iniated by the hydrocoele. 



No secondary twisting of the various part., of 

 the star occurs aeoi its relation to tL; larv» remains 

 constant s« It *-gan, and throughout t!*« life history 

 of the species the following statements hold truer- 

 ventral and lores 1 in the larvs are equivalent tc 

 oral and abcral in the adult. Although no physio=- 

 logical differentiation exists, if we regard that 

 part of the adult as anterior which wasantsriorly di- 



N 



rected in the larva^the trivium is anterior the bivium 



is posterior. 



