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 the front, driving the blood forward. The blood contains bodies corresponding to the white corpuscles of human blood, but lacks the red corpuscles and the red color. The blood is sent even to the wings. The ribs on the wings consist of blood tubes inclosed in air tubes, so that the blood vessels are surrounded by air, and the purification of the blood is taking place throughout the course of the circulation. Hence the imperfect circulation is no disadvantage. The perfect provision for supplying oxygen explains the remarkable activity of which insects are capable and their great strength, which, considering their size, is unequaled by any other animals.

The Nervous System.—The heart in backboned animals, e.g. man, is ventral and the chief nerve trunk is dorsal. As already stated, the heart of an insect is dorsal; its chief nerve chain, consisting of a double row of ganglia, is near the ventral surface (Fig. 131). All the ganglia are below the food tube except the first pair in the head, which are above the gullet. This pair may be said to correspond somewhat to the brain of backboned animals; the nerves from the eyes and feelers lead to it. With social insects, as bees and ants, it is large and complex (Fig. 132). In a typical insect they are the largest ganglia.

of a beetle.

The Senses.—The sense of smell of most insects is believed to be located in the feelers. The organ of hearing is variously located in different insects. Where is it in the grasshopper? The organs of