. La biologie d'eau douce. Biologie des eaux douces. La biologie d'eau douce de l'eau. Tout comme l'obscurité. Certains des moins les espèces nocturnes, comme Leptophlebia et Choroterpes essaim, dans la lumière du soleil à l'abri des lieux de danse en fin d'après-midi, ou de haut en bas entre les ombres et la lumière du soleil mixte sous les couronnes de verdure, de grands arbres forestiers. Les femelles de Baetis ramper sous les pierres à la surface de l'eau et de déposer leurs oeufs dans une seule couche patches juste sous la surface. La vie adulte des éphémères est vraiment éphémère et s'inquiète de filiale à la reproduction ; et la lutte

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. Fresh-water biology. Freshwater biology. FRESH-WATER BIOLOGY. water just as darkness falls. Some of the less nocturnal species, as Leptophlebia and Choroterpes, swarm out in the sunlight in sheltered places of late afternoons, or dance up and down among the mixed shadows and sunlight beneath the canopied crowns of tall stream-side forest trees. The females of Baetis creep beneath stones at the surface of the water and deposit their eggs in single-layered patches just beneath the surface. The adult life of Mayflies is truly ephemeral and is concerned wholly with reproduction; and the struggle for existence is transferred largely to the immature stages. The nymphs are highly and independently speciahzed. They are adapted to all sorts of aquatic situations. A few, like Hexagenia, Ephemera, and Polymitarcys (Fig. 1359), are burrowers beneath the bottom silt. A few, like Caenis and Ephemerella, are of seden- tary habits and live rather inactively on the ^^''- ^f, 5;^, J, ^j^X^'' °' bottom, and on silt-covered stems. Many are active climbers among green vegetation; such are Callibaetis and Blasturus; and some of these can swim and dart about by means of synchronous strokes of tail and gills with the swiftness of a minnow. The species of Leptophlebia love the beds of slow-flowing streams, and all the flattened nymphs of the Heptageninae hve in swiftly mov- ing water, and manifest various degrees of adaptation to withstand- ing the wash of strong currents. The form is depressed, and margins of the head and body are thin and flaring, and can be appressed closely to the stones to deflect the current. So diverse are the nymphs in form that the genera may be distinguished among them by a beginner more easUy than among the adult Mayflies. Mayfly nymphs feed largely on dead vegetable substances —- the decaying stems and leaves of aquatic plants. They are of first importance in the food of fishes. But we are as yet largely in ignorance of the conditions that make for their abund

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• bookcentury1900
• bookdecade1910
• booksubjectfreshwa
• bookyear1918