54 ANATOMY OF THE ENOPLA. 



all covered with vibratile cilia. M. de Quatrefages thus describes only four coats, viz., mucous, 

 internal longitudinal, 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 occur in this 

 organ . 



b. Middle Region of Proboscis. 



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 marginal stylet-sac, and a central 

 (at a, Plate XII, fig. 1), in the pit of the cavity, connected with the reservoir. The walls of the 

 proboscis undergo a considerable change in this division, especially with regard to the deeper layers. 

 Externally the investing coat from the anterior region is continued on the commencement of the 

 reservoir (Plate XIII, fig. 10), and has a crenated border in the contracted state of the parts, with 

 transverse markings or rugse ; but this appearance does not of necessity indicate the presence of 

 circular fibres, for the contraction of the longitudinal layer underneath would cause even a very 

 feebly elastic coat to assume similar markings. The thin subjacent layer of longitudinal fibres is 

 likewise continued to a similar extent on the reservoir, and assists in connecting the divisions. 

 These two layers lie exterior to the stylet-sacs. 



The structure of the pit or termination of the anterior chamber (77, Plate XII, fig. 2) requires 

 special notice. The large glandular papillae of the inner wall gradually diminish in size, as before- 

 mentioned, until the floor is covered only by small, densely arranged and minutely granular 

 processes, giving the surface, which in the ordinary state of the parts bends backwards all round 

 the stylet in the manner shown in the figure, a smoother appearance. The fibres also become 

 firmly bound together, so as to constitute a sphincter for the aperture, and gently curving out- 

 wards and backwards, are lost in the obscurity of the parts caused by the external circlet of 

 glands, somewhat behind the anterior termination of the wedge-shaped investment of the apparatus 

 at the base of the stylet. This floor of the chamber is composed of a series of muscular fibres, 

 whose direction, in the ordinary state of the parts as a transparent living object, is outwards and 

 backwards, but which assume various aspects during the motions of the organ. Thus the floor 

 passes from the conical form with the apex directed backwards to that of a transverse platform ; and 

 in the everted condition has the shape of a cone the apex of which is directed forward (Plate XIII, 

 fig. 14). In the latter position the secure binding of the fibres which surround the central aper- 

 ture just permits the stylet to project, and no more. The whole arrangement constitutes a large 

 muscular pit with very powerful and mobile walls, capable of many and varied alterations 

 of form. In firm contraction of the region the floor of the chamber is pouted forward 

 (Plate XIII, fig. 7), causing a radiated appearance of the fibres, which thus slant outwards and 

 backwards from the central point. A firm constriction of the tube often takes place at the anterior 

 border of the stylet-region, separating the pit of the organ from the more villose or glandular 

 portion in front, and making a double swelling of the parts. Immediately before the marginal 

 stylet-sacs lie some coarsely granular glands, which, however, are less conspicuous than in N. gracilis 

 and others. Prof. Keferstein speaks of this region as having only a longitudinal muscular coat 

 (though the crenated border of the anterior chamber is continued thereon in his figure), and as 



