holes in the earth, and form them into cells; others build nests of extraneous substances, such as bits of wood and leaves; others roll up leaves into cases, which they close with the most curious art; others build a house of mud, and line it with the cotton of trees, or the petals of the most delicate flowers; others construct cells, of secretions from their own bodies; others form cocoons, in which they undergo their transformation; and others dig subterraneous galleries, which, in their complexity of arrangement, in solidity, and in complete adaptation to their purposes, vie with the cities of civilised man. The contrivances by which insects effect these objects have been accurately observed and minutely described, by patient and philosophical inquirers, who knew that such employments of the instinct with which each species is endowed by its Creator offered the most valuable and instructive lessons, and opened to them a wide field of the most delightful study. The construction of their habitations is certainly among the most remarkable peculiarities in the economy of insects; and it is of this subject that we propose to treat under the general name, which is sufficiently applicable to our purpose, of Insect Architecture. In the descriptions which we shall give of Insect Architecture, we shall employ as few technical words as possible: and such as we cannot well avoid, we shall explain in their places; but, since our subject chiefly relates to the reproduction of insects, it may be useful to many readers to introduce here a brief description of the changes which they undergo. [Illustration: Magnified eggs, of _a_, _Geometra armillata_; _b_, of an unknown water insect; _c_, of the lacquey moth; _d_, of a caddis-fly (_Phryganea atrata_); _e_, of red under-wing moth (_Catocala nupta_); _f_, of _Pontia Brassicæ_; _g_, of the Clifden Nonpareil moth.] It was of old believed that insects were produced spontaneously by putrefying substances; and Virgil gives the details of a process for _creating_ a swarm of bees out of the carcase of a bull; but Redi, a celebrated Italian naturalist, proved by rigid experiments that they are always, in such cases, hatched from _eggs_ previously laid. Most insects, indeed, lay eggs, though some few are viviparous, and some propagate both ways. The eggs of insects are very various in form, and seldom shaped like those of birds. We have here figured those of several species, as they appear under the microscope.