BRITISH NEMERTEANS. AND SOME NEW BRITISH ANNELIDS. 381 



section having the same histological characters as in Ommatoplea. At opposite 

 or nearly opposite poles of the circle, however, a remarkable interposition severs 

 the continuity of* the layer (as seen at g, g'). At one pole, two symmetrical 

 bundles of fibres spring from the succeeding circular layer, and, slanting out- 

 wards, cross each other in such a manner as to disconnect the longitudinal coat 

 just mentioned, and for a portion of its circumference wedge it between two 

 bands of circular fibres. The outer or oblique bands of circular fibres become 

 lost in the external coat of the organ. The longitudinal layer (b) is thus 

 diminished to a blunt point on each side of the crossing of these peculiar fibres, 

 and a region is formed externally which is occupied by a special and somewhat 

 lozenge- shaped group of longitudinal fibres, through which the dotted line g 

 passes. The longitudinal layer, especially near the wedge-shaped ends (where 

 the fibres are often grouped in a thicker mass in these preparations, is marked in 

 the centre by a faint linear streak, as if composed of two layers, but this does not 

 continue all round, and is not apparent in every specimen, nor in B. olivacea. 

 At the other pole there is a variation in this arrangement, for it is found that an 

 elongated portion (g') is cut off without apparent crossing, the ends of the great 

 longitudinal coat (b) being widely apart. It generally happens that towards this 

 side the bulging of the contracted organ occurs, and, it may be, such forces the 

 edges of the longitudinal coat apart, and aids in causing the above appearances; 

 but it would not account for them all. In contraction this coat is sometimes 

 thrown into a silky belt of regularly waved fibres. Within the longitudinal layer 

 is an equally powerful belt of circular fibres (c) which, at opposite poles in the 

 transverse sections, gives off the peculiar oblique bands previously mentioned. 

 A basement-layer (d), better marked in this species than in the common form 

 (B. olivacea), is situated on the inner surface of the latter. There is also present 

 in this species an incomplete belt of longitudinal fibres (e) within the basement- 

 layer, and which is not evident in the species just mentioned. Attached to the 

 inner surface of the basement-layer, or in the latter case partly to the incomplete 

 longitudinal layer, is the glandular mucous coat (/), which, from lengthened 

 preservation, has in this case become somewhat altered. The glandular bodies 

 are scattered chiefly towards its inner or free surface. In fresh preparations, i.e., 

 in those made from the organ immediately after extrusion from the living animal, 

 a very pretty radiated arrangement of this coat is constantly observed, as if a 

 series of explosions had occurred in the mucous substance so as to scatter the 

 globules and gelatinous bands in a fan-shaped manner. Indeed, the aspect 

 resembles thick and graceful tufts of grass with large spikes, for the granular 

 glands are mostly at the tips of the streaks of mucus, a state doubtless due to 

 their passage outwards under compression. Prof. Keferstein* figures this in 



* Op. cit. taf. v. fig. 16. 

 VOL. XXV. PART II. 5 E 



