229 



Ophionereis squamulosa (and doubtless many other Ophiurids), in which 

 also the larval skeleton has disappeared completely, no trace of the Plu- 

 teus-form remaining. In these latter larvae ciliated rings are formed, as in 

 the barrel-shaped larvae of Comatulids and Dendrochirotes, and in the 

 pupa-stage of other Holothurians. 



The existence of a true pupa-stage in Ophiurids was first shown by 

 Caswell Grave ^). (Very likely the larva, in which the rearrangement of 

 thevibratile band into an indication of rings was observed by Grave, was 

 a species of the type described here as Ophiopluteus opulentus). My own 

 observations in the main agree with those of Grave, however, differing 



Fig. 102. A. Ophiopluteus Metschnilcoffl (after Metscli nikof f); B. Ophiopl. Claparedei (after 

 Claparede; modified so as to represent tlie larva in ventral view); C. Ophiopl. elongatus 



(after Krohn). 



from them in some minor points. I find the rings less distinctly indicated 

 than shown by Grave, which may, however, be due to my not having ob- 

 served the metamorphosing larvae in the same lateral position as that in 

 which they are represented in Grave' s fig. 8, but from the ventral or dorsal 

 side. The anterior "ring" I have not found to be complete, but it may very 

 well be so in a later stage of metamorphosis such as that figured by Grave, 

 the stages in which I have noticed this rearrangement of the vibratile band 

 being less advanced (PI. XXIX, Fig. 3; PI. XXX, Fig. 2). 1 have been 

 able to ascertain that the anterior band of the "pupa"-stage is derived 

 directly from the preoral band of the larva. Another interesting fact is 

 that in some cases, at least, the vibratile band of the posterolateral arms 

 in an advanced stage of metamorphosis coalesces in the midhne of the 

 larval body, below the developing Ophiurid; how far this is a general rule 

 remains to be ascertained. 



1) Caswell Grave. On the occurrence among Echinoderms of larv* witii cilia arranged 

 in transverse rings, with a suggestion as to their significance. Biol. Bulletin. V. 1903. p. 173. 



