Class-book of physiology : for the use of schools and families : comprising the structure and functions of the organs of man, illustrated by comparative reference to those of inferior animals . ns. 277. The nervous system of in-sects whose actions are generallyenergetic and rapid, and in whichthe apparatus of motion (wings andlegs) is highly developed, presentsa marked difference from that ofthe Mollusca, which are usuallyinert and sluggish. It consists of alarge ganglion in the head, analo-gous to the brain of vertebratedanimals, and a chain of ganglia, onefor each segment of the body, uni- F
Class-book of physiology : for the use of schools and families : comprising the structure and functions of the organs of man, illustrated by comparative reference to those of inferior animals . ns. 277. The nervous system of in-sects whose actions are generallyenergetic and rapid, and in whichthe apparatus of motion (wings andlegs) is highly developed, presentsa marked difference from that ofthe Mollusca, which are usuallyinert and sluggish. It consists of alarge ganglion in the head, analo-gous to the brain of vertebratedanimals, and a chain of ganglia, onefor each segment of the body, uni- Fig< system of a»ted by a double cord, as in. fig. 44. lNSKCT- In the larva or caterpillar, before it is changed into the per-fect insect, the nerves arising from the ganglia are chieflydistributed to the muscles of the legs, and the ganglia areonly repetitions of each other, being nearly of uniform size;but in the perfect insect, the wings and legs, which con- What is said of the ganglia in the higher orders of animals? How doesthe nervous system of insects compare with that of the Mollusca? Of whatdoes the nervous system of insects consist 1 How are the ganglia united ?. 124 CLASS-BOOK OF PHYSIOLOGY. statute the apparatus of locomotion, are confined to thethorax, and the segments of the abdomen have no , the ganglia of the thorax, in the perfect insect,are found to be very much increased in size, and sometimesconcentrated in one mass, while those of the abdomen aremuch smaller. 278. This difference is shown infig. 45, where A represents the nerv-ous system of the caterpillar, fromwhich is produced a species of sphinxor hawk-moth, and B that of the mothitself. In B, the cephalic-ganglion is much larger than that of A, since ithas become connected with more per-fect eyes and other organs of ganglia which supply the wingsand legs (those next below that of thehead) are also greatly enlarged andconcentrated, while the abdominalganglia are d
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