ABSTRACT
Temperature is a factor of great importance in determining the distribution of animals. There are many references in ecological literature to a correlation between distribution of animals and the temperature conditions prevailing in the habitats occupied by the animals. Particular instances of this correlation are the distribution of stream turbellarians (Steinmann, 1906; Thienemann, 1913) and the effects of abnormal temperature conditions on local faunas (Allee, 1923; Stephens, 1938). The great significance of temperature to the animals themselves is shown by the many physiological studies of its action on living matter (Bélehrádek, 1935), and is also evident in the ecologists’ use of the terms stenotherm and eurytherm. This correlation between temperature and distribution has rarely, however, been investi-gated from the experimental standpoint. One line of approach has been the experimental investigation of the thermal resistances of animals from different habitats.
I am indebted to Dr D. E. Kimmins of the British Museum for the identification of some of the species.
The supply of animals was insufficient to test the resistance of Caenis sp. at 26° C. Fig. 1 makes it clear that the thermal index would probably be higher than 26·6° C. if there were a point for 26° C.
