Entomology : with special reference to its biological and economic aspects . ology 27 III. Development 146 IV. Adaptations of Aquatic Insects 184 \\ Color and Coloration 193 \l. Adaptine Coloration 216 All. Origin of Adaptations and of Species 237 AlII. Insects in Relation to Plants 252 IX. Insects in Relation to Other Animals 276 X. Interrelations of Insects 307 XI. Insect Behavior 345 XII. Distribution 366 XIII. Insects in Relation to Man 393 Literature 409 Index 467 ENTOMOLOGY CHAPTER I CLASSIFICATION At the outset it is essential to know where insects stand inrelation to other animals. Art
Entomology : with special reference to its biological and economic aspects . ology 27 III. Development 146 IV. Adaptations of Aquatic Insects 184 \\ Color and Coloration 193 \l. Adaptine Coloration 216 All. Origin of Adaptations and of Species 237 AlII. Insects in Relation to Plants 252 IX. Insects in Relation to Other Animals 276 X. Interrelations of Insects 307 XI. Insect Behavior 345 XII. Distribution 366 XIII. Insects in Relation to Man 393 Literature 409 Index 467 ENTOMOLOGY CHAPTER I CLASSIFICATION At the outset it is essential to know where insects stand inrelation to other animals. Arthropoda.—Comparing an insect, a centipede and acrayfish with one another, they are found to have certainfundamental characters in common. All are bilaterally sym-metrical, are composed of a linear series of rings, or segments,bearing paired, jointed appendages, and have an externalskeleton, consisting largely of a peculiar substance known aschitin. If the necessary dissections are made, it can be seen thatin each of these types the alimentary canal is axial in position;. Diagram to express the fundamental structure of an arthropod, a, antenna; al,alimentary canal; b, brain; d, dorsal vessel; ex, exoskeleton; /, limb; n, nerve chain;s, subcesophageal ganglion.—After Schmeil. above it extends the dorsal blood vessel and below lies theventral ladder-like series of segmental ganglia and pairednerve cords, or commissures; between the commissures thatconnect the brain and the subcesophageal ganglion passes theoesophagus. These relations appear in Figs, i and 163. ENTOMOLOGY Fig. 2. Furthermore, the sexes are almost invariably separate and theprimary sexual organs consist of a single pair. No animals but arthropods have all these characters, thoughthe segmented worms, or annelids, have some of them—forexample the segmentation, dorsal heart and ventral nervous chain. On account of thesecorrespondences and for otherweighty reasons it is believedthat arthropods have de-scended from
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