Life in Lakes and Rivers. T. Macan T.

who have not had a biological training, and who have studied only vertebrates. The number of different kinds – or species to use the proper term – is usually much greater in an invertebrate than in a vertebrate group and, since the animals are so much smaller, the differences are less obvious, and sometimes undetectable by the naked eye. Many people are surprised to learn that the word mosquito, for example, covers in Britain no less than forty different species. We have endeavoured to give some idea of the scope of the freshwater fauna by mentioning the number of known species in each group.

      Latin names are unavoidable, since only a few species have an English name. Invertebrates are usually referred to by two names, and the first of these, the genus or generic name, corresponds to the surnames in the human community; though the Smith difficulty has been avoided by making a rule that the name of every genus must be different. The second name is the species name, and, like our Christian names, many are used over and over again; for example, lacustris