ABSTRACT
The oxygen consumptions of the small ephemerid nymphs Ephemerella ignita and Coenis sp. are (anaesthetised at 10° C.) 950 and 290 c.mm./gm./hour. Their habitats are respectively a stream and a pond.
The oxygen consumptions of the large ephemerid nymphs Ecdyonurus venosus, Ephemera danica and E. vulgata are (anaesthetised at io° C.) 604, 370 and 278 c.mm./gm./hour. They live, respectively, under stones in a swift stream, burrowing in sand in a stream, and burrowing in mud in a pond.
Ecdyonurus venosus is less resistant to oxygen deficiency than Ephemera danica and E. vulgate; and Baetis rhodani (swift stream) is less resistant than Chloeon dipterum (pond).
Fox and Simmonds (1933) called this larva Molanna sp., but subsequent identification of the imago has shown that it is really Limnophilia vittatus.
Throughout this investigation, and that of Fox and Simmonds (1933), the Barcroft apparatus was shaken at a uniform rate, namely thirty complete excursions per minute, the extent of each excursion being four centimetres.
Dr O. Löwenstein, working in this laboratory, found that the nymphs of Rithrogena semicolorata from Frankley were rapidly killed by 0·5 per cent, urethane. This precluded a comparison of their oxygen consumption with that of Ecdyonurus and Ephemera. It is remarkable that animals so closely related as Rithrogena and Ecdyonurus should show such different sensitivities to a narcotic.
