EIJPLECTELLA. Do 



be normally moved off' towards the external surface, finally to 

 take a position at the extreme outer end of tlie distal rays of 

 tlie dermalia (PI. Y, fig. 36). Aualogous to the rhabditi of 

 Turbellarians, the floricomes originate in deep parts and shift 

 themselves over to the most superficial situations to effectively 

 discharge their function as defensive weapons. This point in their 

 history seems to have been hitherto entirely overlooked. As is 

 well known, it is usual to find a floricome to the tip of each 

 dermal hilt-ray on depressed and therefore more protected parts 

 of the external surface ; whereas on more exposed parts, as on 

 the ledges, it is frequently missing or exceedingly rare. 



The graphiocoine may fairly be said to be tolerably constant 

 in Exipledella, notwithstanding it has not yet been discovered in 

 certain species {E. regalis, cucumer, suberea, jovis &■ crassislellaia). 

 I think that at least some of these species may yet be discovered 

 to be not totally wanting in the said rosette. Whenever present, 

 it is found, like the floricome, exclusively in the external trabec- 

 ular layer. A remarkable fact, which has not been noticed by 

 previous writers, in connection with the rosette in (piestion, is, 

 that the sheaves of the fine needle-like terminals are exceedingly 

 liable to break off close to the discs at the outer end of the 

 principal rays, after the rosette has attained its full size. I 

 believe that this breaking off is in fact a normal process, by 

 which the rhaphides — a name that has been given to the liber- 

 ated terminals without the knowledge of their genetic connec- 

 tion with the graphiocome — are put in a position to be moved 

 off, with one of their ends pointed outward, towards the external 

 surface, probably by the same force that drives the Horicomc in 

 the same direction. Finally they are found in the most peri- 

 pheral positions on the wall either scattered or in groups and 



