Gaily Marine Laboratory 7 St, Andrews. 13 



The tentacles" (PI. I. fig. 3, t.) belong to the branchial 

 system, and separate in such a form as this and probably 

 in all or many Sabellids, along with the branchiae, which in 

 their normal line of separation show a notch between the 

 symmetrically curved chordoid basal support, which unites 

 the halves above the gap by a firm bar of similar tissue. 

 A little beyond the outer edge of this bar on each side 

 springs a tentacle, the spout-shaped external basal fold of 

 which is deeply pigmented with brown in Bispira. The 

 inner basal web of each runs forward on the first dorsal 

 branchia, whilst the outer web forms a free flap, the important 

 furrow from the base of the branchial fan lying between 

 them, and it is this groove which is pigmented. The tentacle 

 itself is continuous with the inner flap or base, and presents 

 a somewhat thicker median rib supported by the chordoid 

 skeleton, the whole tapering to a delicate tip. Its nerve is 

 of considerable size, and the organ is probably of great 

 importance in regard to the nature and contents of the 

 currents swept through the groove. Claparede * applied the 

 term " tentacle " to the inner lateral fold of the mouth in 

 his sections, but such is a wholly different structure from 

 the tentacle as here described, and performs a different 

 function. 



In transverse section the tentacle, when fairly formed, 

 presents a rounded axial region and two flaps or lamellae 

 arranged in opposite curves (PI. I. fig. 7). The curves of 

 the lateral flaps or wings are diagnostic, and indicate special 

 functions, one flap curving to the left of the central region 

 and the other more or less to the right in transverse section. 

 Over the whole is the cuticle, then a layer of short nucleated 

 epithelium resting on a basement-tissue, and within it a 

 consistent connective tissue and probably muscular fibres, 

 though these are indistinct on the wings. The central region 

 is more or less rounded in section, with a tough cuticle and 

 thinner hypodertn, but it is supported by a transparent 

 skeletogenous axis containing a homogeneous substance 

 surrounded by granules, whilst on one side (that furthest 

 from the curved flaps) is a band of muscular fibres and on 

 the other a nerve. The fact that this homogeneous substance 

 does not stain would point to its solidity or coagulability. 

 It is noteworthy that in the marginal line of filaments 

 counected by the " perichondria^' strand, similar appear- 

 ances, without the granules, in section are found, so that 

 the tinted centre may be of the same " perichondral " 



* Annel. S6dent. pi. i. fig. 1, tt. 



