374 SCALISETOSITS COMMUNIS. 



Body somewhat elongated, narrowed posteriorly, from ^ to f inch in length, though 

 sometimes longer. Segments from twenty-two to forty-two. Colour pale yellowish 

 throughout, in some faintly marked with brown towards the posterior end, especially 

 between the feet. In others the dorsum is speckled with brownish spots, arranged trans- 

 versely, and numerous yellowish specks. The naked portion behind the scales (including 

 the bases of the feet) is speckled with yellowish and whitish. In some Scotch examples the 

 dorsum is of a blackish hue, interrupted by numerous fine transverse lines, most marked 

 at the segment-junctions. In others a distinct band of dark pigment, interrupted by 

 numerous pale striae, most marked at the segment-junctions, passes along the dorsum. 

 The ventral surface is pale. The segmental eminence is prominent, but the papilla is 

 very small. Posteriorly the body terminates in two caudal styles. 



Proboscis. — In extension this organ in the preparation shows apparently thinner 

 walls than in the ordinary forms. A wide canal thus exists in the centre, and the teeth 

 of the dorsal and ventral arches are widely separated. The usual nine papillae occur on 

 each arch. The teeth are pale brown (amber-coloured). 



Scales (Plate XXXIII, fig. 7) cover the dorsum in front, but leave the centre bare 

 posteriorly. The normal number seems to be eighteen pairs, but few examples are 

 complete in this respect. They are more or less rounded or ovate translucent organs, 

 so that their minute structure is readily shown. The entire scale is minutely dotted, and 

 its areolae so arranged that the whole has the aspect of a transparent plate. The dots, 

 as Ehlers stated, appear to be in the cuticular layer of the under surface of the scale. 

 The outer and 'posterior portions of the scale, moreover, are studded dorsally with a 

 series of small papillae (modifications of cilia) of a cylindrical or clavate outline, many of 

 which run iii the lines of the finely branched nerves. In life these structures have 

 minute papillae or palpocils at the top, so that they probably perform the function of 

 special tactile organs, as indeed the able description of Ehlers would lead us to expect. 

 Only a small portion at the anterior and inner area of the scale is devoid of them, and 

 the nerves seem to terminate there in special end-organs. In addition, a series of much 

 larger clavate processes occurs thinly scattered over the same region (outer and 

 posterior), the largest sometimes projecting at the posterior border. They are readily 

 seen under a lens, standing out like minute pillars from the surface of the scale. These 

 receive nerve-twigs from the main branches, as shown by De St. -Joseph. The outer 

 and posterior borders, further, are beset with a closely arranged series of short globular 

 cilia, which also occur on the surface adjoining the edge. Many of these have micro- 

 scopic papillae (modifications of palpocils) at the tip, and .all show a minutely granular 

 central area — connected by the pedicle with the central connective tissue. 



The nerve- supply of these organs is clearly outlined, as originally described by 

 Ehlers, and subsequently by Langerhans. At the posterior border of the scar for the 

 pedicle an enlargement (ganglionic) occurs, from which a main stem, rapidly breaking 

 up into branches, proceeds posteriorly, giving off twigs in a somewhat dichotomous 

 manner to the greater part of the scale, while a considerable branch goes forward, or 

 obliquely forward and outward, to complete the distribution. The smooth pale area at 

 the anterior and inner border has the smallest branch, probably because its functions 

 are less prominent. The nerve-twigs terminate in peculiar granular swellings — men- 



