Although the head is apparently a single segment, it is really composed of six or seven body segments greatly modified and firmly fused together. Note that it bears a pair of large _compound eyes_ and three much smaller _simple eyes_ or _ocelli_. TECHNICAL NOTE.--Strip off a bit of the outer covering of a compound eye, mount on a glass slide and examine under the microscope. Note that, as in the crayfish, each compound eye is composed externally of many small hexagonal _facets_, the outer covering, the _cornea_, being simply the cuticular covering of the body, in this place transparent and divided into small facets. Besides the eyes, the head bears also several movable appendages, namely the _antennæ_, and the _mouth-parts_. Note the number, place of insertion, and segmented character of the antennæ. These antennæ are sense-organs and are used for feeling, smelling, and, in some insects, for hearing. Note that the mouth-parts consist of an upper, broad, flap-like piece, the[10]_labrum_; of a pair of brown, strongly chitinized, toothed jaws or _mandibles_; of a second pair of jaw-like structures, the _maxillæ_, each of which is composed of several parts; and of an under, freely-movable flap, the _labium_, also composed of several pieces. Each maxilla bears a slender feeler or _palpus_ composed of five segments. The labium bears a pair of similar palpi, which are, however, only three-segmented. The mandibles and maxillæ, which are the insect jaws, move laterally, not vertically as with most animals. Make drawings of the lateral aspect of the head; of a bit of the cornea; of the dissected out mouth-parts. Of the three segments of the thoracic region of the body, the most anterior one is called the _prothorax_. It is freely movable and has a large hood or saddle-shaped piece, the _pronotum_, on its dorsal aspect, and a blunt-pointed tubercle on the ventral aspect. The foremost pair of legs is attached to the prothorax. The next segment is the _mesothorax_, which is immovably fused to the next thoracic segment. What appendages does it bear? The third segment is the _metathorax_, which besides being fused with the mesothorax in front, is similarly fused with the foremost abdominal segment behind. What appendages does the metathorax bear? Examine one of the fore legs and note that it is composed of a series of unequal parts or segments. The segment nearest the body is sub-globular and is called the _coxa_; the second segment is smaller than the coxa and is called the _trochanter_; the third, known as the _femur_, is the largest of all; the fourth, _tibia_, is long and slender; and the next three, the last of which is the terminal one and bears a pair of claws and between them a little pad, the _pulvillus_, are called the _tarsal segments_. Most insects have five tarsal segments. Note the great size of the hindmost or leaping legs. Determine the segments of the middle and hindmost legs. Make a drawing of a fore leg.