LETTERS FROM ALABAMA. 
169 
forests, where they bore holes in the timber by- 
chiselling the wood with their conical jaws ; the 
eggs are laid, the young grow up and become 
pup80 in the heart of the tree, from whence the 
perfected beetle issues to pursue a similar course. 
Acuteness of vision appears not to depend on the 
size of the compound eye, which merely affects the 
extent of the visual horizon, but upon the depth 
and number of the optic tubes^ whose convex extre- 
mities form the facets of the eye. These tubes in 
the Longicorn beetles are by no means numerous, 
in proportion to their extent of surface, but few 
and large ; so large as to be quite visible in the 
greater species to our unassisted sight, the large 
eyes being perceptibly netted, like those of the 
dragon-fly, while the eyes of other beetles appear 
to the naked eye quite smooth and shining. It 
would seem, then, that a wide range of vision is 
granted to these insects to enable them to discover 
the trees suited to their wants, but that no great 
discrimination being required as to what particular 
spot of the trunk shall be attacked, they need not 
and have not this sense minutely distinct and 
accurate. 
Some very fine Lepidoptera have fallen under 
my observation lately. The Arched Swallowtail 
(Papilio Calchas) begins to be frequently met with; 
it is about four inches and a-half in spread of wing ; 
black on the upper surface, with three rows of yel- 
low crescents on the front pair, and on the hind 
two rows, and a broad band of yellow across the 
middle. Beneath, the front pair are as above, but 
the hind wings have the band divided into large 
and regular crescents, forming a third series, and 
all the rows are beautifully tinged with orange; 
