PLUMES OF CEPHALODISCUS. 241 



of developmeut represented iu figure j has been reached the 

 buds migrate. Whatever be the explanation the fact remains 

 that from an abundant supply of buds of various stages I 

 have only discovered one which shows pinnules in a further 

 stage of development than that drawn in figure J. The bud 

 is figured in the 'Report on Cephalodiscus' ("Discovery " 

 Expedition, PI. 1, fig. 68). It has fourteen plumes, of 

 approximately the same size and development, standing for- 

 ward in a bunch, parallel with one another; the stalk of the 

 bud is no longer terminal, but projects from the ventral 

 surface of the " body." Two of the plumes of this bud are 

 shown in text-fig. 7, k and l ; k is a nearly dorsal view, L a 



Text-figuke 8. — Diagrammatic representation of tlie view ob- 

 tained on lookinj^ backward at an adult ])olypidc of Ceph alodiscus 

 n is r esc ens after cutting short the plumes and post-oral lamella, 

 and removing tiie buccal shield. The cut bases are represented in 

 black, po.l. Tiie edge left after clipping away the post-oral lamella. 

 1, 2, 3, 4, 5, 6 and 7. The stumps of the several plume-axes, showing 

 the grooves facing away from the middle of the ellipse upon which 

 they are set. /j.s. Stalk of the buccal shield, c.n.m. Position of 

 central nerve mass, ni. Mouth, a. Anus. The arrows indicate 

 the direction of the food currents from the grooves of the plumes 

 into the mouth. This figure is in the main similar to Harmer's 

 figures of C. levinseni (' Pterobranchia of the "Siboga" Expe- 

 dition,' 1905, pi. 12, figs. 158 — 160), but it is treated more dia- 

 grammatically. 



nearly lateral view. The plume-axis is very massive and 

 pigmented, and has a smooth hemispherical extremity; some 

 of the other plumes of this bud, however, have the ends less 

 rounded, more like those of J. There are about seventeen or 



