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 setse of An- 

 nelids, with which they have nothing in common. Biirger ('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 a clam 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 5 to 10 mm. 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 ^, its 

 height averages 15 /x, and the thickness varies from 7 to 8 /a. 



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 lamellae 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). 



