INSECTS : 'WINGS AND THEIR APPENDAGES. 



77 



narrow, sometimes irregular and unequal, and of various 

 other indescribable outlines. Perhaps the most common 

 forms are ovate, heart-shaped, and that of the pan of a 

 fire-shovel. Each thin scale has a minute foot-stalk, 

 which is not connected with it at either extremity, but at 

 a point of one surface a little way from the smaller end, 

 whence it projects at an oblique angle ; so that when the 

 stalk was inserted in its proper cell in the skin of the 

 insect, the scale lay horizontally, covering the insertion. 

 This is a peculiarity not found in 

 some other scales that I shall pre- 

 sently introduce to you. 



The whole body of the scale is 

 traversed by a series of fine close- 

 set parallel lines, running longitu- 

 dinally 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 

 imaginary central line, towards which 

 they respectively converge, 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 below. Be- 

 tween the ribs, on the larger scales, we see a number of 

 very delicate cross lines, which are probably regular 

 wrinklings of the depressed surface. 



There is another little Insect of the same family, com- 

 monly found in cupboards, 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 

 elide. Here, while the general appearance and structure 

 agree with those of the scales which we have just been 



SCALE OP BRISTLE-TAIL. 



