BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 321 



The foregoing description of the structure of this region differs much from that 

 given by M. de Quatrefages, almost the only author who has entered into the 

 minute anatomy of the Ommatoplean proboscis. He states, like Mr H. Goodsir,* 

 that externally the tube is furnished with a series of transverse muscular bridles, 

 which maintain it in position within the body of the worm, and he gives a section 

 of the parts in Nemertes balmea, which bears out his description very well ; but 

 he did not observe that if such bridles exist, they would have to pass through 

 the muscular sheath in which the proboscis glides, before reaching the body-wall 

 of the animal. Apparently he has not made out the two diverse structures. His 

 minute anatomy of the proboscis is chiefly taken from the examination of 

 Borlasia Angliw, and hence cannot apply in any degree to the Ommatopleans, 

 though he considered it the type of both. He makes out only two muscular layers 

 in the wall of this organ, and though in his section from B. Anglice he indicates 

 "traces de fibres transversales, 1 ' by a few lines crossing these longitudinal coats, 

 he distinctly observes that they are not apparent in the smaller species. These 

 longitudinal coats are separated, says he, by a transparent homogeneous tissue, 

 which forms a great number of bridles of very elastic fleshy columns, making, in 

 other words, an elastic cellular layer ; and he figures this in the before-men- 

 tioned section, adding that this lax cellular coat will give the two longitudinal 

 muscular coats that independence of action necessary for the proper perform- 

 ance of their functions. No such cellular layer has been seen in the British 

 species, but between the two longitudinal coats there is found the remarkable 

 reticulated layer. He mentions a transparent homogeneous coat within his longi- 

 tudinal muscular layer, corresponding to the mucous coat of the higher animals, 

 and adds that the papillse of the latter are all covered with vibratile cilia. M. 

 de Quatrefages thus describes only four coats, viz., mucous, internal longitu- 

 dinal, elastic cellular, and external longitudinal ; and if the stays or bridles 

 which he notes as connecting the tube to the body-wall be taken into account, 

 it may be surmised that the muscular sheath for the proboscis is included in 

 his reckoning. No cilia are present in this organ. Professor Keferstein does 

 not enter into the structure of this region in Ommatoplea. 



Middle Region. — The elongated chamber just described terminates posteriorly 

 in a sort of cul-de-sac, into which three small apertures converge — one at each 

 side from the lateral stylet-sacs, and a central one in the pit of the cavity con- 

 nected with the peculiar reservoir which succeeds. 



The walls of the proboscis undergo a considerable change in this region, 

 especially in regard to the deeper layers. Externally there is the investing 

 coat continued from the anterior region on to the commencement of the reservoir 

 (Plate IX. fig. 11), and which hasacrenated border in the contracted state of the 



* Ann. Nat. Hist. xv. 1845. 

 VOL. XXV. PART II. 4 N 



