. The biology of dragonflies (Odonata or Paraneuroptera). Dragon-flies. 252 COLORATION [CH. D. The Head Pattern (fig. 116). We shall only mention here two striking formations which illustrate the effect of the marginal and central type of pattern, respectively, on the head. 1. The Post-ocular Spots of Agrio- nidae. The formation of these by stages from an original marginal epicranial pattern is illustrated in fig. 116 a. 2. The T-mark on the Frons in Aeschninae and Lihellulidae. The form- ation of this mark by stages from an original central frontal pattern, and its subsequent reduction to a &
. The biology of dragonflies (Odonata or Paraneuroptera). Dragon-flies. 252 COLORATION [CH. D. The Head Pattern (fig. 116). We shall only mention here two striking formations which illustrate the effect of the marginal and central type of pattern, respectively, on the head. 1. The Post-ocular Spots of Agrio- nidae. The formation of these by stages from an original marginal epicranial pattern is illustrated in fig. 116 a. 2. The T-mark on the Frons in Aeschninae and Lihellulidae. The form- ation of this mark by stages from an original central frontal pattern, and its subsequent reduction to a "clear" front (usually yellow), is illustrated in fig. 116 B. The jewelled frons appears to have been produced by an exactly opposite process, extension of the ground-colour, instead of reduction. Indications of the original marginal or central type may also be found by studying the clypeus and B. Fig. 116. Colour-patterns of the head. A. Four stages in the development of the brilliant postocular spots of Agrioninae from an original marginal t5rpe. b. Four stages in the development of the T-mark and of the "clear" frons from an origi- nal central type. Original. We can profitably conclude our account of the Body-Coloration of Odonata by appending a short table of the principal types of colour-pattern. Marginal Types Type Marginal-'gy/.°"';,^°^«^ '^ (Heuochromes Annulo-marginal ^ gj^ochromes ° I Heiiochromes Tricolorous (Heiiochromes) Metallic Unicolorous Group Petalurinae Agrionidae Goniphi7tae, Petalurinae Agrionidae, some Lestidae and Calopterygidat Some Agrionidae Calopterygidae, Lestidae Central Types / Hylochromes ^ , , ' Aphantochromes j Bicolorous Heiiochromes (Unicolorous Heiiochromes Annulo-central (Hylochromes) Metallic Unicolorous Aeschninae, Synthemini, Macromiini Some Brachytronini, Aeschna, Gynacantha Libdhdinae, Eucorduliini Libellulinae Tetrathemini, Macromiini, Cordulegastrinae, Cordulephyini Eucorduliini, a few Libellu
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