EVENINGS AT THE MICROSCOPE 



sect, the scale lay horizontally, covering the insertion. 

 This is a peculiarity not found in some other scales that 

 I shall presently introduce to you. 



The whole body of the scale is traversed by a series of 

 fine close-set parallel lines, running longitudinally from 

 end to end. At least this is the ordinary arrangement; 

 but occasionally you see scales, in which there are two 

 series of parallel lines, arranged on either side of an imag- 

 inary central line, toward which they respectively con- 

 verge, but never, I think, diverge from it. These lines 

 appear to form thickened ribs, but 

 seem to be made by elevations of 

 the membrane both above and be- 

 low. Between the ribs, on the larger 

 scales, we see a number of very deli- 

 cate cross lines, which are probably 

 regular wrinklings of the depressed 

 surface. 



There is another little Insect of the 

 same family, commonly found in cup- 

 boards, and in chinks of old damp 

 houses, and called the Sugar-louse (Lepisma); very much 

 like this, but of a silvery lustre, and carrying the three 

 bristles of the tail diverging widely. This also is covered 

 with scales, some of which are preserved on this glass 

 slide. Here, while the general appearance and structure 

 agree with those of the scales which we have just been 

 considering, there is considerable diversity in details. The 

 form is usually ovate or shovel- like; the foot-stalk, project- 

 ing at a similar angle, is not set on the inferior surface, 

 but in the bottom of a deep narrow incision; and the ribs 

 are invariably divergent like those of a fan. In these, 



SCALE OF BRISTLE-TAIL. 



