1/4 CASWELL GRAVE. 



as are found in ophiuran plutei are developed, although at one 

 time I mistook the beginnings of the skeletal plates of the adult 

 for such. The anterior end of the larva is produced into a long 

 preoral lobe about which two ciliated rings are developed. The 

 posterior end is enlarged and contains the various internal struc- 

 tures of the larva and developing ophiurid. The mouth is ven- 

 tral and interrupts the third ciliated ring of the larva (numbered 

 4 in Fig. 5). The fourth ring (5) surrounds the posterior end. 

 The dorsal pore is situated at the point indicated by the small 

 x between ciliated rings 3 and 4. As development progresses 

 the preoral lobe diminishes in size until finally it is entirely ab- 



3 



4 



FIG. 6. Older larva of Ophiura brevispina. Original. The change in position 

 which takes place in the ciliated ring (5) is shown. 



sorbed. During late larval life a change in the arrangement of 

 one of the ciliated rings also takes place. The ring numbered 5 

 becomes interrupted on the ventral side and takes on a more 

 definite relation to the mouth (see Fig. 6). 



In 1900 I found a second ophiuran larva at Beaufort which, in 

 its metamorphosis from the pluteus to the radial form, showed the 



