Nervous System--The Head--Eyes--Compound and Simple--Uses and Powers--Sir John Lubbock's Experiments--The Antennæ--Structure and Uses--Mouth--Detailed Description. Before proceeding to detail the most important facts connected with the internal economy of the hive, it will be desirable to describe with some minuteness the physiology and anatomy of the inhabitants, so that it may be more easy to understand the means by which various processes are accomplished, and the most important events of the community are brought about. Much that has been hitherto said will become more readily comprehended by attention to the structure of the various organs we are now about to describe. It will hardly be necessary to enter into a more minute account, than we have already given, of the egg, the larva, and the pupa. We shall, therefore, confine ourselves to detailing the most interesting points in the physiology of the perfect insect. It has been noted, in an earlier chapter, that the members of this division of the animal kingdom are characterised by having three very distinct segments in their bodies the head, the thorax, and the abdomen. As the nature and arrangement of the nervous system forms one of the soundest bases of classification in the highest of the three kingdoms in nature, we shall first direct attention, in each case, to this all-important matter of detail. [Illustration: Fig. 22.--Nervous System of Privet Hawk-moth.] [Illustration: Fig. 23.--Nervous System of Larva of Bee.] The general arrangement of the nerve-matter in the sub-kingdom _Articulata_, to which all true insects belong, is that of a double cord, with knot-like protuberances, called _ganglia_, at more or less regular intervals. The two filaments are in some cases close together: in others, quite distinct; while the larger nerve-masses--the previously mentioned _ganglia_--also vary in juxtaposition, according to the greater or less importance of the functions they regulate. In the illustration of the larva of _Sphinx ligustri_ (the privet hawk-moth) (Fig. 22), the nervous cord is nearly uniform throughout its length, though at its upper portion a separation takes place into three loops. The ganglia also occur at almost equal distances. A very similar disposition of the nerve-structure is seen in the larval condition of the bee; but we may note the absence of loops, the larger development of the cephalic masses, without the separation of their filaments to inclose the gullet together with a more plainly-defined distance between the cords which run parallel through the rest of the body. [Illustration: Fig. 24.--Nervous System of Perfect Insect.]