Now let us unpin our Beetle, turn it on its back, and examine it from the under side. Head, thorax, and abdomen may be made out more clearly than before, and we can see that the last two regions are divided into segments. Let us deal with the head first. This may be easily separated from the thorax with a dissecting needle, or with a pocket-knife--an exceedingly handy tool. The huge goggle-eyes cannot escape observation; and, even without a magnifier, they may be seen to be compound--that is, made up of a number of facets, which show like a fine network. Just in front of the eyes are the antennae, which serve as organs of touch and perhaps also of other senses. Kirby has recorded facts which seem to show that the antennae (in some cases) are also organs of hearing. Other authorities, after many observations, have come to the same conclusion. The matter, however, is beset with difficulty. It is certain that some Insects have their ears in their legs; and for the present, at any rate, we may be satisfied to know that the antennae are sense-organs, certainly of touch, probably of smell, and, in some cases, of hearing. An excellent authority on the subject is Sir John Lubbock’s book, _The Senses of Animals_[11], which contains references to very many original papers. [Illustration: FIG. 21. FIG. 21.--Upper surface of head of Dytiscus. _a_, labrum, or upper lip; _b_, clypeus or shield; _c_, mandible dissected out, and (_d_) reversed; _e_, eye; _f_, antennae.] [Illustration: FIG. 21 A. FIG. 21 A.--Under surface. _a_, mentum or chin; _b_, ligula or tongue; _c_, labial palp; these three together forming the labium, or lower lip; _e_, eye; _f_, antennae. Above the maxillae, or lower jaws (_d_ _d_), are shown dissected out: _d^1_, inner or palpiform lobe; _d^2_, maxillary palp; _d^3_, lacinia or blade; _d^4_, the palpifer or piece that bears the palp (_d^2_); _d^5_, stipes or stalk; _d^6_, the cardo or hinge.] Now we may pass to the mouth parts. It will be good practice to dissect these out, either in air or in water. We may hold a Beetle between the finger and thumb of the left hand, and separate all the parts with a needle held in the right. It is a good plan to gum these parts on a card, for comparison with the figures in our favourite book--whatever that may be--on Natural History, and also with the mouth parts of insects of other Orders. For however much these may differ in form, and in the uses to which they are put, they are really modifications of the same parts.