185 
length observed was 1°5mm. The pinnules are arranged in 
two rows along the axis, and there are from 25 to 30 in each 
row. Those near the tip are usually short, but not always as 
short as those shown in text-fig. 2. The longest pinnules 
occur at about one-third of the length of the plume-axis from 
the base, and these measure about ‘4mm. in length. The tips 
of the pinnules are very slightly enlarged, and are frequently 
found incurved. 
General Internal Anatomy.—The general internal anatomy 
of Cephalodiscus dodecalophus has been worked out in great 
detail by Harmer, Masterman, Schepotieff, and others,* and 
in the monograph on Cephalodiscus in the Report of the 
‘Discovery ” (Antarctic) Expedition I have given a series of 
diagrammatic sections of the body of C. mgrescens, taken 
through structures of particular interest, which with the ac- 
| W) 
A RS Ss | 
Text-Fic. 2. A,—side view of a moderately expanded plume of Cephalo- 
discus gilchristi ; the pinnules of one side only are shown. B,—exceptional 
form of termination of the plume-axis ; cases of swollen terminations such as 
this are rare. C,—end portion of a normal plume seen from the aponeural 
aspect. (>< 50-) 
companying text afford a tolerably complete account of the 
anatomy of that species. As compared with these two species, 
the polypide of C. gilchristt does not present any striking 
peculiarities, and this being so, it does not call for a detailed 
description. The following have been recognised in sections 
of the polypides of C. gilchrisiz, and they so closely resemble 
their equivalents in the earlier investigated species of Cephalo- 
discus that they may be dismissed with a mere mention :—a 
pair of proboscis canals, a pair of collar canals, collar-canal 
muscle (cross-striped fibres), a pair of gill slits, pleurochords, 
post-oral lamella, divisions of the coelom, coelomic trabeculz, 
muscles of the buccal shield, of the collar region, trunk region 
and stolon, and nerve tracts. 


*A full bibliography is given in the Report of the “ Discovery 6 Expedition. 
