56 W. G. RIDEWOOD. 



pinnules except the few youngest at the base of the plume-axis are slightly 

 swollen at their extremities. The most distal pair of pinnules arise as a rule 

 immediately to the proximal side of the end-bulb, and are comparatively short 

 (figs. 33-35, plate 5) ; exceptionally they arise from the end-bulb itself (fig. 36). The 

 longest pinnules vary from '5 to '7 mm in length in different individuals. 



The bulb at the extremity of the plume-axis of C. dodecalophus is a hollow 

 enlargement, of the shape of two-thirds of a sphere, and with a wall composed of 

 taller epithelial cells than those of the plume-axis. The cavity is continuous 

 with that of the plume-axis, and is traversed by a few coelomic trabeculae. 

 These end-bulbs have been described in detail by Masterman (22, p. 344, 

 and 24, pp. 516 and 521) and Cole (2). The former author regarded the 

 terminal swelling of the plume as a rudimentary monostichous compound eye, 

 bearing a remarkable resemblance, both in appearance and structure, to the 

 " branchial organs " found in the sedentary Annelids, such as Potamilla and 

 Sabella, but he states in a later paper (28, p. 725) that he had already 

 abandoned this view before the publication of the observations of Cole, who 

 considers the terminal bulb to be a " rhabdite-battery," composed of rhabdite 

 " cells " resembling those of Turbellaria and Nemerteans. 



Harmer (10, p. 38) states that end-bulbs with highly refringent vesicles, 

 similar to those of C. dodecalophus, occur in the buds of C. gracilis on the 

 first pair of plumes, sometimes also on the second and third (p. 20 and p. 94), 

 and that these vesicles probably disappear as the adult stage is reached. No 

 end-bulbs or refringent vesicles occur in C. levinseni, nor in neuter individuals 

 of C. sibogae, but the males of C. sibogae have two long arms, representing 

 the first pair of plume-axes without pinnules, and these have closely-set refringent 

 vesicles covering the greater portion of their length. On page 90 he suggests, 

 with some diffidence, that possibly the vesicles " have the nature of reserve 

 supplies of nutritive material, developed precociously in the young bud for the 

 nutrition of the future testes." 



The end-bulbs of C. hodgsoni are less truly spherical in their curvature than 

 are those of C. dodecalophus, since the tall epithelium extends farther along the 

 neural than the grooved face of the plume-axis, and thus present a lop-sided 

 appearance when examined from the side (figs. 33 and 35, and text-fig. 1). The 

 clear refractive beads of previous authors occur among the tall cells of the end-bulb, 

 and are present in greater profusion in immature than in full-grown polypides. 



A minute examination of thin sections and of teased preparations suggests the 

 possibility of the refringent vesicles of Harmer and the rhabdite " cells " of Cole 

 being the globules of the tubarium of the colony in process of secretion, like the 

 globules of mucus in the goblet-cells of a mucous membrane. When the secretion 

 is forming, it is of course, surrounded by protoplasm, and if the bead of secreted 

 material is large, it will bulge upon the surface, being covered by a thin pellicle 



