The food and feeding mechanism of Chloeon dipterum L. and Baetis rhodani Pictet, (Insects, Ephemeroptera) - A field and laboratory study.

A detailed account is given of the structure of the mouthparts of Chloeon dipterum L. and Baetis rhodani Pictet, with a description of the mode of functioning based upon direct observations and the anatomical findings. Differences in the feeding apparatus are correlated with differences in the conditions under which the two species feed. The musculature of the mouthparts is compared with that of other genera of Ephemeroptera, and some of the changes that have been involved in the evolution of flattened forms such as Eodyonurus are suggested. Three kinds of variation in the food - 1. Seasonal, 2. Local, 3. Between lorvas of different sizes - were investigated by analysing the gut contents of samples of larvae taken at fortnightly intervals from three ponds and streams over a period of eighteen months. Existing techniques of food analysis are reviewed and a quantitative technique is described in which an estimation of the error in the results is possible. Descriptions of the habitais are given and the causes of variations in quantity and composition of the food ingested are discussed. The results are given of an investigation of the ability of C. dipterum and B. rhodani to ingest and digest algae in the laboratory. The presence of viable cells in the gut was detected by culturing the material on a medium suitable for algal growth.