38 



of the opercLilum, in order to shew its relations to the food-grooves of the arms. It must be 

 realized that the food-groove of the sixth arm passes towards the axis of the projected spiral, 

 at a deeper level than that shewn in the figure. The free edge of the opercukim (which is 

 continuous with the sixth arm) is thus represented as starting too near the dorsal middle line. 

 It will further be apparent from the actual frontal sections that the cavities of all the arms 

 pass into the genera! collar-cavity which is situated at a lower level than (in reality, posterior 

 to) the portion of body-wall which is formed by the continuous dorsal surfaces of the arms in 

 the diagram. 



Although fig. 159 is thus not an exact representation of the collar of C. levinseni^ it 

 is, I believe, correct as a diagram. The possible relations of the arrangement here shewn with 

 the lophophore of Plioronis will be considered later. 



C. sibogae. 



In the neuters of this species the relations of the collar resemble those already described 

 in the other species. There are, however, only four pairs of arms (PI. VIII, fig. 93; PI. IX, 

 fig. 97), while the operculum (PI. IV, fig. 40 ; PI. VII, fig. 78; op^i is very large. The collar 

 is moreover provided with specially strong muscles, the relatively high development of the 

 muscular .system being marked in both the collar and the metasome of this species. 



The peculiar features of the male will be considered in Section X\". The remarkable 

 arms (PI. VII, figs. 72 — 76, 79; PI. IX, figs. 95, 96, 99) are only two in number. They are 

 circular in section (fig. 79) except close to their base, where a vestige of a food-groove persists, 

 leading by means of a food-channel (fig. 79, f.c.r.,f.c.l.) to the mouth, which is shewn in 

 fig- 95- The male has no operculum. 



E n d - b u 1 b s. 



Each arm in C. dodecalophtis terminates, as is well known, in a globular end-bulb, which 

 possesses remarkable refringent vesicles. These structures were described by M'Intosh (87, p. 11) 

 as glandular in nature. Masterman (97, 2, p. 344) sugge.sted that they are compound eyes, 

 a view which he subsequently discarded (03, p. 725). Cole (99) regards them as rhabdite- 

 producing organs. 



I have myself no evidence which decides the function of the end-bulbs, although I refer 

 to the subject again in describing the males of C. sibogae (Sect. XV), in which refringent vesicles 

 are present in extraordinary numbers along the whole course of the arms. The bulbs are 

 conspicuous structures in the buds of C. gracilis, where they seem to be invariably present at 

 the ends of the arms of the first two pairs, while they may also occur on the third arms. I 

 have no evidence that they are found on the fourth and fifth arms, while it seems probable 

 that the vesicles may completely disappear from all the arms of some of the adult specimens, in 

 this species. I have not found di.stinct end-bulbs or refringent vesicles either in the neuter 

 individuals of C. sibogae or in C. levinseni. 



