MICROSCOPIC DRAWING AND ENGRAVING. 
Fig. 32 
and for the various organs supplied to it by nature for the gratifi¬ 
cation of its ravenous propensities. It may be truly affirmed 
that no similar creature is provided 
with weapons of destruction so power¬ 
ful, so numerous, and so perfectly 
adapted to their end ; it is on this 
account, that the insect, in this first 
state of its existence, has been vulgarly 
called the “water-devil.” Its length, 
when full grown, is about an inch and 
a half, and the strength, courage, and 
ferocity with which it attacks small 
fish and other aquatic animals larger 
than itself, are truly surprising. 
50. The representation of this crea¬ 
ture, in its natural size, when young, and before it has reached 
its full growth, is given in fig. 33. 
51. The magnified representation of it given in fig. 34, 
has been engraved from Dr. Goring’s drawing. 
52. In the first months of Spring, small nests con¬ 
taining the eggs of these insects, may be seen floating 
among the weeds, in stagnant pools; they are formed 
like balls, of a dusky-white colour, and silky texture; 
they are attached to the roots or stalks of weeds at the 
bottom of the water by a thin stem of the same material 
as the nest, but stronger and more dense. Thus placed, they 
remain during the winter preserved from the eflects of cold, even 
when the surface of the water is frozen over; since by a natural 
thermal law the temperature increases in going downwards.* 
Early in spring, the stem or thread by which they are attached to 
the weeds, is broken by the winds, and the nest being detached and 
lighter, bulk for bulk, than the water, rises by its buoyancy to the 
surface, where being exposed to the warmth of the sun as the season 
advances, the eggs are hatched. The larva, however, after breaking 
the shell, is still confined in the bag-shaped nest; it accomplishes 
its liberation by gnawing a hole in it, from which escaping, it dives 
immediately to the bottom, eagerly devouring all the small aquatic 
insects that fall in its way. If, however, it should happen that 
there is a short supply of this food, the voracity of these creatures 
is such, that they fall upon and devour each other. 
53. When the larva is very young, measuring not above a quarter 
of an inch in length, it is sufficiently translucent to enable an 
observer to see its internal structure with the microscope, by light 
* See Tract ©n “Terrestrial Heat,” also Handbook of Natural Philosophy, 
“Heat.” 
