646 EXTERNAL ANATOMY OF INSECTS. 
are intirely denuded. With regard to szze, the scales vary 
often considerably in different tribes ; in Heliconia they 
appear to be more minute than in the rest; and in Cas¢- 
nia they are the largest and coarsest; the extremity of the 
wings of Lepidopterous insects in general is fringed with 
longer scales than their surfaces, and even those of the 
last in the same wing sometimes vary in magnitude. The 
little seeming tooth that projects from the middle of the 
posterior margin in the upper wings of Notodonta, is 
merely produced by some longer diverging hairs. ‘The 
shape and figure also of scales are very various—some 
being long and slender; others short and broad ; some 
nearly round; others oval, ovate, or oblong; others 
spathulate; others panduriform or parabolical; some 
again almost square or rhomboidal; many triangular ; 
some representing an isosceles triangle, and others an 
equilateral one; lastly, some are lanceolate and others 
linear ; again, some have a very short pedicle and others 
a very long one: with regard to their extremity ; some 
are intire, without projecting points or incisions, while 
others are furnished with them: of these some terminate 
in a single long mucro, others have several shorter ones; 
some are armed with teeth, varying in number from two 
to thirteen in different species*. Many other forms 
might-be enumerated, but these are sufficient to give 
you a general notion of the infinite variety of this part 
of the works of the Creator. I must next say a word 
or two upon their arrangement on the wing. In most 
* De Geer has given 34 figures of different scales (1. £. iii. f. 28); 
and in Pirate XXII. Fic. 6. a—w. 22 others, collected from Reau- 
mur, are given. Mr. Brown showed me some scales under a very 
powerful microscope which were divided longitudinally by many 
ridges or furrows, traversed by numerous transverse ones. 
