336 FUNAFUTI ATOLL. 



extend on to the lateral walls of the heart-bladder, and also in 

 front of the heart-bladder form a vertical sheet, the fibres of 

 which converge to be inserted directly into the limiting membrane 

 of the apex of the "notochord" (Plate xix., fig. 6, dsc.). From here 

 also fibres arise which diverge downwards and forwards on each side 

 of the ventral septum. The ventral septum, accompanied by 

 fibres of the muscle plate, passes obliquely downwards and 

 forwards from the anterior end of the " notochord," its most 

 anterior ventral point of afiix being a considerable distance in 

 front of the apex of the " notochord." Behind the apex of the 

 " notochord," the ventral fibres of the plate are inserted into 

 the limiting membrane on its ventral surface, on each side of 

 the attachment of the ventral septum (fig. 1, vps. and dsc.). The 

 splanchnic epithelium of the proboscis ccelom (fig. 1, sp.) has 

 the usual relations. As in P. minuta and P. australiensis, the 

 splanchnic epithelium is covered by a layer of spongy tissue repre- 

 senting the inner limiting layer of the connective tissue of the 

 proboscis. 



As in other species, a free space representing the proboscis 

 ccelom is present round the central organs. The ventral septum 

 (fig. 1, vps.) has oblique anterior and posterior free edges (fig. 2, 

 vps.). Behind its posterior free edge there is an unpaired ventral 

 pocket (fig. 3, vp.) which ends blindly in what appears to be 

 simply the thickened basement membrane of the epidermis below 

 the anterior portion of the proboscis skeleton (fig. 4, vp.). 



The dorsal proboscis pockets (tigs. 2 and 3, dp.) separated by 

 the heart-bladder, pass backwards, and, on a level with the posterior 

 end of the unpaired ventral pocket, each becomes constricted to 

 form a small and short ventral canal (fig. 4, dp.) which ends 

 blindly, and a much larger dorsal canal, the proboscis canal (pc.) 

 The two proboscis canals may either open into each other, thus 

 forming a single canal which opens to the exterior by a single 

 median proboscis pore, or the canals may remain separate and 

 open independently to the exterior, thus forming two proboscis 

 pores, one on each side of the median line (fig. 5, p.'). 



" Notochord." The " notochord " has the usual Ptychoderan 

 shape. Anteriorly it appears, in section, of an oval outline, with 

 a large central lumen. In the region of the ventral blind sac, it 

 is markedly extended transversely and somewhat dorso-ventrally 

 compressed (fig. 2). From the lumen of the blind sac there pass 

 forwards two short lateral horns (fig. 2, Ib.) as in P. australiensis. 

 In the posterior portion of the proboscis neck, the " notochord " 

 is also dorso-ventrally flattened. Its dorsal wall is here much 

 thicker than the ventral, and provided with numerous glands. 

 The ventral wall shortly in front of the opening of the " noto- 

 chordal" lumen into the throat becomes reduced to a low layer of 

 columnar or cubical cells resting on the proboscis skeleton. 



