250 



THE MECHANICAL FUNCTIONS. 



Fig. 164 exhibits some of the more usual shapes as they ap- 

 pear when viewed with high magnifying powers. 



Each scale is inserted into the membrane of the wing by 

 a short pedicle, or root, and overlaps the adjoining scales: 

 and the wliole are disposed in rows with more or less regu- 



"^ V ^ 



larlty; one row covering the next, like tiles on the roof of a 

 house.* This imbricated arrangement, together with the 

 marks that are left on the membrane of the wing where the 

 scales have been rubbed off, are shown in Fig. 165, which 

 is a faithful delineation of the appearance of the wing of the 

 Hesperia Sloanus, seen through a powerful microscope. 

 The membrane of the wing itself, when stripped of its 

 scales, is as perfectly transparent as that of the bee, and is, 

 in like manner, supported by diverging nervures. Many 

 butterflies exhibit in some parts of the wing smooth pearly 

 spots, called by entomologists, ocelli, or eyes, which arise 

 from those parts being naturally destitute of scales. The 

 number of these scales necessary to cover the surface of the 

 wings must, from their minuteness, be exceedingly great. 

 The moth of the silk worm {Bornbyx mori, Fig. 148,) 



* The scales on the wing of the Leplsma are of two kinds; one set being 

 arranged in rows, as usual, and the otliers, which are of a different shape, 

 being inserted between and over the former, so as to fasten each firmly in its 

 place. 



