NATURAL HISTORY. 13 
unassisted eye, resembles a species of down, or 
mildew, surrounding the animal. If touched 
with the point of a feather, the mass becomes 
whiter and diminishes in magnitude. The cause 
of this change is readily discovered under the 
microscope. In the first instance, the parasites 
were extended at the extremity of the filament 
that attaches them to the animal, and conse- 
quently dispersed over an extensive surface; in 
the latter case, they approach the animal by 
bending or coiling the connecting filament, and 
_ thus reducing the size of the mass. 
Our knowledge of the transformation of 
these aquatic coleoptera is very limited; Resel 
and Swammerdam are the only naturalists that 
have left any record of their change; and even 
their accounts are partly conjectural. They 
state, that the larve, when mature, bury them- 
selves in an oval cavity formed in the earth on 
the sides of their natal ponds or marshes, and 
there undergo their first change into a chrysalis, 
and after remaining a proper time in this quies- 
cent state, emerge from the earth a perfect 
beetle. The appearance of the complete insect 
has no resemblance to that of the larva; indeed, 
so different are they in the two states, that not 
only have casual observers been deceived, but 
Dr. Shaw informs us, that even the early writers 
