president’s address. 
471 
2. Temperature. 
The influence of temperature and climate on animals is great 
and obvious, and with most species there is a well-defined range 
of temperature within which life and growth are possible, the 
life range being very much greater than the growth range. 
But the aspect of the question with which we are concerned is 
not that of the degrees of temperature but rather with the 
seasonal range of it. In the sea the temperature conditions, 
owing to the great body of water and its continual movement, 
reach the maximum of seasonal uniformity, whereas the 
temperature of fresh water usually closely reflects the changes 
in the temperature of the air. The conditions in this respect in 
fresh water and in the sea resemble the contrast between a 
continental and an insular climate, 1 the former being exposed 
to extreme range and fluctuation of temperature, while the 
latter is comparatively uniform. So severe are the fluctuations 
of temperature (with which may be associated evaporation) that 
many fresh water invertebrates of temperate climates have been 
compelled to evolve protective devices to tide them over evil 
times. It is to meet such vicissitudes that the cyclic reproduc- 
tion of the Cladocera, for example, has arisen, the rapid asexual 
multiplication of the favourable periods being followed by a 
short period of sexual reproduction and the laying of eggs 
which have the power of retaining vitality even when dried 
and frozen. In the case of some Phyllopods it is, if not 
necessary, at least very favourable to the hatching of these 
eggs, that they should be so dried and frozen, and they can 
retain their vitality, when kept dry, for many years. The eggs 
of Branchipus are said not to develop without having been 
first dried and then placed in water, but it has been found 2 that 
the same result is attained if the eggs are placed for a time in 
salt solutions which extract water from them. 
The importance generally of an uniform temperature is 
shown by the fact that certain animals (Holothurians, for 
example), which live near the surface in the Tropics, live also 
l. Von Martens. Ann. Mag. Nat. Hist.. 1858. 
2. Abonyi. Allat. Kozlem. Budapest 9, 1910. 
