812 INSECTA. 
Besides tne secreting organs proper to nutrition and generation, others are 
found in certain insects for secreting fluids, either calculated for defence, er 
for protecting them from variations of temperature during their transforma- 
tions. The acrid and fetid fluids with which some insects defend them 
selves, are produced by small tortuous tubes, and accumulated in two vesicles 
_ near the anus. 
The Carabi and the Dytiscz secrete acid fluids which redden vegetable blue; 
the Brachinz discharge an acid vapor, which gives considerable pain; a spe- 
cies of Blaps produces a brown fetid oil, which swims upon water ; the 
silk-worm possesses organs for secreting a silky matter of which the threads 
of silk are formed ; and in the Hymenoptera, such as wasps, bees, sphexides, 
&e., the extremity of the abdomen incloses a sting, caftulated for attack or 
defence. This sting is a hollow canal furnished with muscles, of which the 
contraction or dilatation projects, or withdraws it at the will of the animal. 
At the base of this hollow tube is found a gland which secretes the acid or 
poisonous fluid. The sexes in insects are always in separate individuals, 
male and female, and coupling takes place at certain seasons, as in the 
h'gher animals. The only exception to this rule occurs in some genera of 
the order Hymenoptera, where, besides the males and females, a third kind 
of individuals occur called neuters. These, from what has been observed in 
the economy of the bees, who, when a new queen is wanted, rear one of 
the larvee of the neuters for this purpose, and conceived to be imperfectly de- 
veloped females. ‘The males are distinguished from the females, by their 
reproductive organs, by their smaller size, and in general more brilliant co- 
lors; by the form of their antenne, and sometimes by their having wings, 
while the females are apterous. Reproduction takes place in the last or per- 
fect state; and after impregnation, the females, with instinctive sagacity, 
deposit their ova, of various forms, on objects or places where the young 
animal, when hatched, may find its appropriate food. 
Insects are in general oviparous animals; for though a few, which have 
been termed ovo-viviparous, bring forth living larve, as the flesh-fly, or as 
the Hippobosca equina, produce their young in the pupa state; yet, generally 
speaking, the whole class may be considered as oviparous. The ova are of 
two kinds; some with a membranous covering like those of reptiles, and 
the others crustaceous like the eggs of birds. The variety, however, in 
point of form, among these ova, is almost incredible; nearly equal, it may 
be said, to the number of the species. Some are round, elliptical, lenticu- 
lar, cylindrical, pyrarnidal, flat, and even square; some are smooth, others 
figured or grooved; and in point of color every shade is employed, some 
shining with the lustre of pearls, and others with the hue of gold. And 
these ova are all deposited with the most unerring instinct in places where 
the future animal may find its proper food without the parent’s care. 
The number of ova deposited by particular insects is extremely various, 
but in general it may be remarked that the fertility of insects exceeds that 
a 
