98 ANATOMY OP THE ANOPLA. 



surrounds the sheath for the proboscis (Plate XXI, fig. 3), a feature of considerable physiological 

 importance. 1 



In spirit-preparations of Micrura fusca the anterior third, especially if distended by the pro. 

 boscis, is rounded, but the rest of the body has on each side a prominent thin margin, which in 

 transverse section presents a great contrast to the same parts in Z. gesserensis. The muscles on 

 the whole are thicker, and the body more depressed in contraction. The circular muscular coat 

 forms a flattened ellipse. The inner longitudinal layer is much diminished opposite the nerves 

 increases in bulk near the central dorsal region, and again abruptly tapers on each side of the 

 median line, so as to form a broad wedge for the arch of the proboscidian sheath. It also 

 increases in thickness towards the centre of the ventral surface, only a slight concavity occurring 

 at the median point. The external longitudinal coat, however, presents the most typical deviation, 

 for at each side, opposite the nerve-trunks, it extends outwards in the form of a prominent 

 triangular process (in transverse section), the layer being then gradually narrowed towards the 

 dorsal and ventral surfaces. In Micrura fasciolata the brownish-red pigment on the dorsum 

 penetrates even to the circular muscular coat, but at other parts it is confined to the region 

 without the external longitudinal muscular layer. 



The posterior end of the body in Micrura requires special mention, since there is superadded 

 a peculiar attenuate and contractile style. This appendage (Plate XVII, fig. 21) seems to be 

 formed by a prolongation of the cutaneous and part of the muscular (longitudinal and circular) 

 textures of the body- wall of the animal. The entire organ in contraction has a granular appear- 

 ance, the coarsest granules, and occasionally a few circular masses of brownish pigment, being at 

 the tip. Within is a central chamber (a), which undergoes various alterations in size, and 

 contains a transparent fluid. This cavity is not connected with the digestive tract, which opens 

 by a terminal pore (z) at the base of the process, nor can proboscidian discs be seen therein. I 

 have not as yet ascertained with what system it communicates, but its connection with the circu- 

 latory appears most probable. The style is richly ciliated externally, and undergoes many and 

 varied motions, now forming a verrucose knob, now stretched to an extreme degree of tenuity, 

 and apparently assisted in the latter action by the fixing of the tip, the warty formations of 

 which seem to perform the functions of suckers ; for the animal may be observed progressing with 

 a loose style, then the tip of the latter suddenly becomes fixed upon the clean and smooth glass, 

 and the whole organ is gradually elongated. The fixed portion at the tip is usually more dilated 

 than the succeeding part of the style. Prof. Grube thought the caudal process of certain 

 Nemerteans might be due to reproduction of the tail, but, of course, this view is inapplicable to 

 the foregoing. 



a. Body-wall in the Carinellidce. — In Carinella annulata the cuticular cells or areolae are 

 smaller (Plate XVII, fig. 17), but they have the same arrangement, and retain much of their 

 shape after mounting (Plate XXI, fig. 3). The characteristic opaque-white dorsal and lateral 

 pigment-stripes pass throughout the entire dermal tissue, while the white specks on the sides 

 (apparently corresponding with the openings of some of the genital sacs) do not traverse the whole 

 thickness, but lie towards the inner border. 



There are only two muscular layers, an external circular coat (e, Plate XXI, fig. 3), and an 



1 The animal in the British Museum termed " Gordiophis subt err emeus' ' is an ordinary example of 

 the same family. 



