812 INSECTA. 



Besides the secreting organs proper to nutrition and generation, others are 

 found in certain insects for secreting fluids, either calculated for defence, or 

 for protecting them from variations of temperature during their transforma- 

 tions. The acrid and fetid fluids Avilh which some insects defend them- 

 selves, are produced by small tortuous tubes, and accumulated in two vesicles 

 near the anus. 



The Carabi^and the Dytisci secrete acid fluids which redden vegetable blue ; 

 the Brachini 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, 

 &c., the extremity of the abdomen incloses a sting, calculated 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 

 higher 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 larvse 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 antenna?, 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 larvae, as the flesh-fly, or as 

 the Htppobosca 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, pyramidal, 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 And 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 



