MUSEUM OF COMPARATIVE ZOOLOGY. 145 
ficial, and evidently cannot be actively moved by the animal. They 
are in all respects carefully to be distinguished from the sete of An- 
nelids, with which they have nothing in common. Burger (’91, p. 634) 
called attention to the fact that the hairs are hollow, and are purely 
cuticular structures. 
Scales. — One finds on the sides of the male near the posterior end 
numerous scale-like cuticular outgrowths. My attention was first at- 
tracted to them in transverse sections, where they present the appear- 
ance of a tooth (Plate II. Fig. 14). Seen from the surface (Fig. 18) they 
have much the shape of aclam shell. They are found scattered over 
both lateral aspects of the animal, in spots so thickly that from one to 
seven are cut in each transverse section (Fig. 14). They vary much in 
size, the smallest occurring near the beginning and end of the area, 
whereas they are interspersed with larger ones at the centre. The area 
which they occupy begins about 1.2 mm. from the posterior end of the 
body, and extends over 5to 10mm. In general such a scale may be 
said to resemble a narrow clam shell attached along the hinge side 
(Fig. 18). The line of attachment is always parallel to the long axis of 
the body, but the concavity of the scale is directed indiscriminately 
dorsad or ventrad (Fig. 14). The length of the scale is about 40 y, its 
height averages 15 p, and the thickness varies from 7 to 8 p. 
In most transverse sections the external layer of the cuticula is con- 
tinuous over the entire surface of the scale (Fig. 15), and only in cer- 
tain cases can one see that it is interrupted by a minute opening 
(Fig. 16), which is connected with a fine canal. On account of its 
minute size this canal can be traced through its entire length only in 
exceptional cases, and usually appears as a groove at the outer or in- 
ner margin of the scale (Fig. 17). I was unable to find either gland cell 
connected with the canal or sensory filament passing through it. 
The core of the scale is formed of a substance which stains like the 
internal layer of the cuticula, but which is in nearly all sections well 
marked off from that layer. If the scales be treated with caustic potash, 
the core is broken up into lamella by lines which radiate from the apex 
of the scale. In transverse sections, however, the core is marked by 
fibres parallel to the central canal, and thus nearly perpendicular to the 
fibres of the internal layer of the cuticula elsewhere. This difference in 
the direction of the component fibres serves to separate the core of the 
scale from the internal layer of the cuticula in and near the plane of 
the central canal (Fig. 17), whereas elsewhere one finds no definite line 
of demarcation between the two (Fig. 15). 
