. The theory of evolution in the light of facts. rs to the myrmecophil modeof hfe to which they owe their systematic among the other Diptera we meet with manymyrmecophil genera, suchas Microdon, Ephippomyia,Harpagomyia, etc. We come now to the under-lying principle of the aboveexamples. It is based on theevidence of palaeontology,comparative morphology and ?I- 1 J , • T J 1 Fig. 37.—Physogastre Imago of biology, and the mdlVldual Termitoxenia AssmutU. evolutionary history. ^^^^^^ Wasmann.) (a) Palaeontology shows us that the systematic orders of the Arthropods, to which t
. The theory of evolution in the light of facts. rs to the myrmecophil modeof hfe to which they owe their systematic among the other Diptera we meet with manymyrmecophil genera, suchas Microdon, Ephippomyia,Harpagomyia, etc. We come now to the under-lying principle of the aboveexamples. It is based on theevidence of palaeontology,comparative morphology and ?I- 1 J , • T J 1 Fig. 37.—Physogastre Imago of biology, and the mdlVldual Termitoxenia AssmutU. evolutionary history. ^^^^^^ Wasmann.) (a) Palaeontology shows us that the systematic orders of the Arthropods, to which the Ant guests and Termite guests belong, appeared very much earlier in the worlds history than the Ants and Termites themselves. Thus, so we conclude, the guests belonging to those older Arthropod orders could not be absolutely created for their later-coming hosts, but have only later been evolved by way of natural evolution out of originally independent hving forms by adaptation to the myrmecophil or termitophil mode of life into the o 2. 196 THE THEOEY OF EVOLUTION systematic species, genera, and families such_ as wefind to-day. An example out of the class of insects we give inmore detail. The order of the Beetles appeared geo-logically already in the beginning of the Mesozoicgroup of formations in the Trias, where it is representedby about twenty genera. Altogether 352 Mesozoic speciesof beetles have long since been found. ^ The order ofthe Termites (Isopterae) appears, however—so far ashitherto can be certainly known—first in the beginningof the Tertiary period, therefore at the commencementof the Csenozoic group of formations : in the Eocene wefind first one species, in the Oligocene twenty-five, in theMiocene twenty-nine. The family of the Ants of the orderof Hymenoptera, so far as can be certainly known, firstappeared in the lower Oligocene—thus in the olderTertiary period: in the Oligocene there are 121, in theMiocene 174 species—which for fossil insects is
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