Experimental work on Daphnia

[First paragraph...]
The first work on most animals is their discovery and identification. Observations on their natural history follow. From these have developed studies on communities and populations and for freshwater plankton such studies have been intensively carried out for some time. They have resulted in much information about the composition, distribution and growth of the populations, and on fluctuations in populations together with the relation of the fluctuations to the biological and physico-chemical environment. Much work on freshwater Cladocera as populations or communities is being carried out at present and this work fills large sections of general texts on limnology. But only within recent years has much account been taken of the relation of the physiology of the animals to the general effect on the population.