PLUMES OP CEPHALODISODS. 239 



appears comparatively narrow (g and h). The fourth plume 

 in Q is set between the base of the third plume and the 

 anterior part of the free edge of the post-oral lamella, and so 

 when the fifth plume appears (h, 5) it would seem as though 

 that plume must have arisen from the edge of the post-oral 

 lamella itself. Similarly also with the sixth and seventh 

 plumes. 



I have not met with a bud showing the early development 

 of the sixth plumes, so that there is a greater interval than I 

 could have wished between h, with fifth plumes appearing, 

 and J, with seventh plumes appearing. 



Up to the time when the fifth plumes are beginning to 

 develop, the size of the plumes diminishes from the first to 

 the fifth (h), but when the seventh is making its appearance 

 (j) the plumes first formed have failed to maintain their 

 initial superiority in size, and the first five pairs of plumes 

 are nearly of equal size. 



Pinnules arise rather late. In text-fig. 7, J, the seventh 

 plumes have already appeared, and yet the pinnules of the 

 first plumes are not more than hemispherical projections. 

 On the plumes of the first pair the first ten or twelve pairs of 

 pinnules arise simultaneously, the later ones are added at the 

 basal end of the series. In Cephalodiscus hodgsoni 

 (text-fig. 3, o) and Cephalodiscus dodecalophus (text- 

 fig. 4, l) the pinnules on the first plumes are already finger- 

 like projections at the time when pinnules first make their 

 appearance on the fifth plumes, and before the axes of the 

 last plumes (the sixth) have shown signs of development. 

 In Cephalodiscus nigrescens, however (text-fig. 7, j), 

 pinnules begin to appear simultaneously on the first five 

 pairs of plumes, and are very little advanced at a time when 

 the last plumes (the seventh in this species) have already 

 come into existence. The bud from which fig. j was drawn 

 is of the same size and general appearance as that repre- 

 sented in fig. 67 of Plate 7 of the 'Antarctic "Discovery" 

 Expedition Report on Cephalodiscus,' 1907. 



In text-fig. 7, J, the first five plumes have elongated con- 



