340 FUNAFUTI ATOLL. 



in the cellular part of the dorsal nerve, while they are almost 

 entirely absent in the cellular part of the ventral nerve. The 

 course of the ventral nerve (fig. 9, vn.) is marked by a very 

 shallow median groove. 



Laterally to the dorsal median groove, there is on each side a 

 shallower branchial groove, the epidermis forming the lateral walls 

 of which also contains numerous gland cells and stains deeply 

 (fig. 9, brg.). 



The longitudinal musculature (fig. 9, Imt.) follows immediately 

 on the basement membrane of the epidermis. It is interrupted 

 dorsally and ventrally by the dorsal and ventral vessels, and also along 

 the sub-median lines situated close to the base of the lateral wall of 

 the branchial grooves (fig. 9). Numbers of radial fibres pass in- 

 wards from the limiting membrane of the epidermis to be inserted 

 into the walls of the oesophagus and gill pockets. The coelom is 

 here completely subdivided into two, above by the dorsal mesentery 

 and below by the ventral vessel. In mature specimens the lateral 

 halves of the coelom are almost completely occupied by the 

 gonads. 



The alimentary canal is, as in other species of the genus, divided 

 into a dorsal branchial canal (fig. 9, ^.)and a ventral cesophageal 

 canal (ce.). The line of separation between the two is marked by 

 two projecting longitudinal ridges, the limiting ridges (fig. 9, lc.), 

 but in this species these two ridges are widely separated from each 

 other so that the branchial and oesophageal canals are in open 

 communication (fig. 9). 



The epibranchial band (fig. 9, epb.) along the mid-dorsal line of 

 the branchial canal is composed of long narrow cells, and stains 

 only slightly. It contains small gland cells in no great abundance 

 and with no definite arrangement. 



The gill pockets have the same general structure as in P. minuta. 

 The synapticulee of the gill skeleton (fig. 9, sn.) do not exceed 

 thirteen or fourteen in number, those more dorsally situated 

 being usually wider apart than the more ventral ones. The 

 gill pores open into the branchial grooves just mesial to the sub- 

 median lines as in P. minuta, and, as in that form, oblique slips 

 of the longitudinal musculature pass between successive pores. 



In the non-ciliated epithelium of the outer, the anterior and 

 posterior Avails of the efferent portions of the gill pockets, as well 

 as in that of the outer walls of the gill tongues (" tongue bottom ") 

 there occur numbers of gland cells (figs. 9 and 10). The outer 

 wall of the gill tongue (" tongue bottom ") is not enfolded into 

 the cavity of the tongue (fig. 10) as is found to be the case in 

 sections through the gills of P. minuta and P. australiensis. 



