234 



W. G. EIDEWOOD. 



Masterman lias stated ^ that the first three pairs of plumes 

 arise with their grooved faces directed towards the buccal 



Text-figuke 5. — Diagrams showing that the later developed 

 plumes (4, 5 and 6) have their bases set more dorsally than tlie 

 earlier. The heavy dots mark the several plume-bases, the heavy 

 line the line of attachment of the post-oral lamella. In A, a side 

 view of a bud with three pairs of plumes, the plume-bases and tlie 

 post-oral lamella are in one plane, a plane nearly parallel with the 

 buccal shield. In B the base of the fourth plume is more dorsally 

 placed than the others, and the line of the post-oral lamella rises at 

 its anterior end. Similarly with the fifth plume and the post-oral 

 lamella in figure C. In D, a diaj^ram of an adult polypide, the base 

 of the sixth plume is not only dorsal to that of the fifth, but is ante- 

 rior also; the right and left plumes of the sixth pair are thus fairly 

 close together; the line of attachment of the post-oral lamella is 

 produced forward so that the end of the line is, as before, close to 

 the base of the last- formed plume. In D the pinnules are not 

 shown, and the plume-axes are represented very diagrammatically. 



a. Anus. c.p. Collar pore. g.d. Gonad duct. g.s. Gill slit. 

 st. Stolon. Other lettering as before. 



shield, but later rotate upon their axes so that the grooves 



face away from the shield ; further, that the last three pairs 



1 'Trans. Roy. Soc. Edin.,' vol. xxxix, 1S98, p. 521. 



