In the perfect insect we observe some decided modifications to have taken place. The head portions have grown proportionally larger, and show a loop for the passage of the œsophagus, while two large ganglia in the thorax indicate the seat of impressions and impulses connected with the organs of motion--wings and legs--which had no existence in the larval condition. As the functions of the abdominal region, viz., those of digestion and circulation chiefly, remain much the same in the different states through which the individual passes after the hatching of the egg, we find, as we might expect, little change in the nervous system of the posterior segment of the body. From each nerve-mass will be observed filaments branching on either side to the outer edges of the body. By means of these communication is kept up between all parts of the frame. Sensations are received and conveyed to the sensorial organs, and return-stimuli are sent to the organs whose movements depend for regulation on the different ganglia. This branching of the nerve-fibre is directly proportional to the variety and force of the several functions subserved by the various structures to which they proceed. _The Head._--We will now describe in some detail the structure and functions of the highly-important organs contained in the anterior segment, or head. And first in order let us take the _Eyes._--On either side of the head may be observed an oval lobe, convexly rounded and immovable, brown in colour, covered with a horny tunicle, and exhibiting to the unassisted eye a vast number of distinct points. These points, under a high-power magnifying-glass, are seen to be facets, hexagonal in shape, so as to occupy all available space, without interstices, and each connected with a minute tube and a thread of nerve-matter leading to the cephalic ganglia or brain. These compound eyes, as they are called, are common to most true insects. They may be easily seen in flies, bluebottles, moths, butterflies, &c. The numbers of the facets vary greatly in different families of the _Articulata_. In the common house-fly there are, it is stated, about 4,000; in the white cabbage-butterfly, 17,000; in the dragon-fly, 24,000. It has been computed that in each compound eye of the bee there are about 3,500 of them. [Illustration: Fig. 25.--Eyes of a Bee, Greatly Magnified.]