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64 



The three regions into which the segments of the six-legged insects are grouped, are 

 known by the names of the head, the thorax and the abdomen. The head carries the 

 special sense organs, as the eyes, the mouth and the antennae. The eyes are wonderful 

 structures, and are constructed to cover a very large field of vision ; they consist, first of 

 all, of two large compound eyes, made up of numerous small six-sided facettes, which are 

 so numerous that Leeuwenhoec is said to have counted as many as 8000 in the eye of a 

 fly, and Strauss 8820 in that of a cockroach ; besides these two compound eyes, there are 

 in many insects two or more simple eyes (ocelli) arranged across the forehead, they can 

 be easily seen in the common Humble Bee. There are some insects which have only ocelli 

 and even some with no eyes at all. 



The principal organs of the mouth are six in number, two on each side of the open- 

 ing, one above and one below, arranged thus ' \ , the upper single organ is the upper 



lip or labrum, the lower the labium or lower lip, this lower lip has a basal joint (mentum) 

 supporting a more flexible part (ligula) ; the upper or inner integument of the ligula is 

 usually developed into a kind of tongue, which is a distinct part (lingua) in the locusts 

 and dragon flies ; the superior pair of the lateral organs are the upper jaws or mandibles, 

 which are generally hard and serve to tear the food, the inferior pair are the lower jaws 

 or maxillae, which are generally soft and serve to to carry the food to the gullet, 

 to be swallowed. To the lower jaws and under lip are attached short jointed processes, 

 called palpi or feelers. These oral organs are the same in all insects, although the struc- 

 ture is vastly different among those which obtain their food by mastication and those 

 which obtain it by suction ; by dissection and comparative anatomy however it can be 

 shown that they are identical, only greatly modified in form, in both of these classes. In 

 biting insects, as beetles, the side pieces are short, far apart, and have a horizontal motion, 

 and the upper lip is a flat plate closing the mouth above ; with sucking insects as mos- 

 quitoes, the same parts are elongated into lancet-like organs, are close together, and have 

 a longitudinal motion, and the lower lip at the same time is developed into a tube, which 

 incloses them. In Lepidoptera the three upper organs are very feebly developed, while the 

 maxillae are elongated into a delicate proboscis, the identification of which with the 

 maxillae is shown by the occasional presence at its base of a pair of minute palpi ; the 

 lower lip is soldered to the head, but is furnished with a pair of palpi, well developed and 

 clothed with scales, which act as a protection to the proboscis. In the flea the middle 

 lancet seems to represent the upper lip. 



In bees the lower lip and maxillae form together a sucking apparatus, but they are 

 also provided with well developed upper jaws or mandibles. 



In the front part of the face of an insect are two appendages, which vary very much in 

 form, in the different sub-orders and genera, and even in the sexes of one species; they are 

 called antennae. What the exact functions are of these important organs, is not known, 

 but it is probable they have more uses than one. Experiments have been made with 

 moths in which it was observed that if the antennae were removed the insect seemed 

 unable to direct its flight. It is probable too that the olfactory nerve is situated in the 

 antennae. The different forms which the antennae take have been made use of by ento- 

 mologists in classifying insects. 



The next division of the body of an insect is the thorax. This is the solid portion 

 which bears the organs of locomotion, and comprises the three segments which follow 

 the head. The first one is called the pro-thorax and bears the first pair of legs, the next 

 or middle segment is called the meso- thorax and supports the second pair of legs and the 

 anterior pair of wings, the third segment is called the meta-thorax, and to it are attached 

 the third pair of legs and the hind wings. The wings are objects of great beauty and 

 strength, and consists as a rule of a double membranaceous plate, traversed by more or 

 less bony veins. 



The last division of an insect's body is the abdomen, which consists of a series of 

 segments attached by membranes. Each of these segments is formed of two arcs or 

 semi-segments, one above and the other below. The abdomen is the seat of the organs 

 of reproduction and alimentation. The senses of insects are dependent upon the nervous 

 system, which consists of a series of nervous masses or ganglia, joined together by two 



