. Outlines of zoology. ine, in arcticregions, in caves. Even on the sea the Challengerexplorers found the pelagic Halobates, a genus of distribution of insects is mainly limited by food-supplies and climate, for their powers of flight are oftengreat, and their opportunities of passive dispersal by thewind, floating logs, etc., are by no means slight. Many insects are more or less parasitic, either externally 3S8 PHYLUM ARTHROPODA. as adults, fleas, lice, bird-lice, plant-lice, etc., or in-ternally as larvae, the maggots of bot-flies in sheep,and a great number of borers with
. Outlines of zoology. ine, in arcticregions, in caves. Even on the sea the Challengerexplorers found the pelagic Halobates, a genus of distribution of insects is mainly limited by food-supplies and climate, for their powers of flight are oftengreat, and their opportunities of passive dispersal by thewind, floating logs, etc., are by no means slight. Many insects are more or less parasitic, either externally 3S8 PHYLUM ARTHROPODA. as adults, fleas, lice, bird-lice, plant-lice, etc., or in-ternally as larvae, the maggots of bot-flies in sheep,and a great number of borers within plants. We need only mention Hessian-fly, phylloxera, Coloradobeetle, weevils, locusts, to suggest many more which are ofmuch economic importance as injurious insects. On theother hand, our indebtedness to hive-bee and silk-moth, tocochineal and lac insects, to those which destroy injuriousinsects, and to those which carry pollen from flower toflower, is obvious. Finally, we must at least mention that in ants, bees,. \„....Fig. i88.—Mosquito.—After Nuttall and Shipley. wasps, and termites we find illustration of various grades ofsocial life, and marvellous exhibitions of instinctive skill aswell as some intelligence. Insects and Disease As carriers of disease-germs insects play a very im-portant part. The role of flies as mechanical distributorsof anthrax, plague, and other bacterial diseases has beenclearly proved. Besides carrying baciUi upon their bodiesai^d leaving them on wounds or food, they also swallowgerms, .and subsequently deposit them in their excreta insimilar situations. Undoubtedly, however, the most seriouscases are those of the blood-sucking Diptera which act as PEDIGREE. 359 hosts as well as carriers of disease-producing gnats or mosquitoes (Culicidae) are perhaps the mostimportant in this respect. Human malaria is conveyed byat least twelve different species of mosquito, of which thosebelonging to the genus Anopheles have the widest dis
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
