338 FUNAFUTI ATOLL. 



Posteriorly the cavity of the heart-bladder is occupied by cellular 

 tissue crossed dorsally by transverse fibres passing between its 

 lateral walls. As in other species its ventral wall (fig. 1, vw.) is 

 provided with a layer of transverse muscular fibres. 



Proboscis Vessels. The glomerulus is shown in transverse section 

 in fig. 1 (gl.). It does not cover the anterior end of the " noto- 

 chord " as in P. minuta and P. australiensis, its two halves being 

 separated by the fibres of the dorso-ventral muscle plate inserted 

 into the apex of the " notochord." The central blood space (figs. 

 1 and 6, cbs.) opens freely on each side into the glomerulus sinus 

 on the lower portion of the lateral walls of the heart-bladder. 

 The efferent proboscis vessels (figs. 2-5, epv.) only become distinct 

 at the posterior end of the glomerulus. They are not joined by a 

 connecting vessel in the proboscis neck as in P. australiensis. 



The afferent (figs. 2-4, av.) and efferent vessels of the subepi- 

 dermic network have the usual relations. 



Along the mid-ventral line of the proboscis there runs a small 

 vessel internal to the circular musculature, which stands at inter- 

 vals in connection with the subepidermic capillary net, the circular 

 muscular layer being interrupted at these points. When the 

 ventral septum appears this vessel apparently passes up along its 

 anterior edge. 



Collar. The five zones of the epidermis (cf. Part I.*) are distinct 

 in longitudinal section. The first zone, including slightly more 

 than the anterior free rim of the collar, and the fifth zone, form- 

 ing the posterior rim of the collar, stain similarly and not very 

 deeply. The second and fourth zones stain deeply, while the third 

 zone stains less deeply. The collar musculature has the usual 

 relations. 



The perihfemal spaces, as in P. sarniensis, aperta, and aus- 

 traliensis, enclose about the ventral half of the collar nerve cord 

 (Plate xx., fig. 7, phs.). 



As may occur in P. australiensis, the dorsal septum of the 

 collar appears as a free fold in front of the first root and reaches 

 the epidermis along with the latter. From here it extends to the 

 posterior end of the collar. The ventral vessel consists of a single 

 fold. It unites either near the mid-region of the collar or nearer 

 its posterior end. with a median subepidermic vessel to form the 

 ventral septum of the collar. The dorsal vessel in the collar 

 occupies the whole of the mesentery between the perihfemal 

 spaces. 



The collar canals (fig. 8, ccl.) have the usual shape and are re- 

 latively short. Each runs obliquely backwards and downwards 

 to become continuous with the anterior wall of the first gill-pocket. 



* Ante, p. 207. 



