REPORT ON PHORONIS BUSKII. 11 



series of meshes, basement-tissue of considerable thickness, and, histly, the ghniduUvr 

 coat, which fills the whole interior. The structure is now joined to the diminishing 

 fundus of the body-cavity, but is wholly separated from the thick basement-tissue of the 

 body-wall, which forms a continuous ring. The next .section (PL II. fig. 4) presents 

 a junction between the basement-tissue of the body-wall and that of the special organ 

 now under consideration, and a lumen appears in the chamber of the latter. The 

 channel then gets outside the basement-tissue of the body-wall, which is incurved to 

 suit the circumstances, and presents, from the arrangement of the tissues, a somewhat 

 reticulated appearance on each side of the latter just as it leaves the body-cavity. It 

 then passes to the exterior at the tip of the body in the form of a duct, having an 

 inverted ^ shape (PI. II. fig. 5), the inner lining of the canal being smooth in section, 

 from the closely arranged cylindrical epithelium, while the surrounding region is 

 composed of the more lax hypoderm of the body-wall. 



In longitudinal sections of those in which the reproductive organs are well developed, 

 the strands of this apparatus lead to the posterior end of the alimentary canal, near which 

 are the masses of the reproductive organs. No distinct lumen exists internally, Ijut 

 such may, of course, appear at intervals. 



The exact nature of this remarkable organ is unknown, further than that it appears 

 to be glandular, and in close relation with the reproductive system ; and it presents a new 

 character in the morphology of the group. Its position would correspond with the pit 

 of the sac, the condition of which is so marked a feature during development {i.e. when 

 the Actinotrocha becomes vermiform). It is possible that it may form an accessory 

 channel for the issue of the ova. The hollow cup-like surface formed by the thickened 

 hypoderm of this surface in some specimens would seem to indicate its use for fixation. 



Tentacles. 

 The tentacles or branchiae arise from the slightly enlarged cephalic end by a some- 

 what firm basal web which is entire ventrally, but is widely split dorsally (PL I. fig. 1), 

 so as to present the aspect of a double fan, as in the Sabellidfe. Indeed, viewed from 

 this surface, each fan or volution is supported on its own basis, which, moreover, is 

 oblique — elevated in the centre, and sloping downward and outward externally. The 

 basal web remains entire for about a third of the total length of the tentacular arrange- 

 ment, and then breaks up into a multitude of simple slightly tapering filaments, which 

 are pale throughout the greater part of their length, but tinted of a dark-brownish hue 

 toward the tip. Externally the surface of each is densely coated with cilia, which are 

 somewhat longer toward the tip of the process. As ordinarily seen in the preparations, 

 the branchial fan performs about three volutions. The skeletal elements of the 

 apparatus ^ commence on the sides of the anterior region of the body as a series of 



'Professor Ray Lankester, in bis article "Polyzoa" in the Eucycloiffidia Britannica, attributes the original 

 description of these to Mr. Caldwell. 



