CRUSTACEANS From a dry county like Warwickshire one might not expect a great abundance of animals so aquatically disposed and so essentially moisture loving as the Crustacea. How small in fact any such expectation has been down to quite recent times is pointedly illustrated by a volume of much merit and usefulness. For the meeting of the British Association in 1886 a Handbook of Birmingham was prepared, embracing a wide range of subjects. The section devoted to zoology occupies in it satisfactory space and prominence. A valuable page of this section is devoted to crustaceans, but the writer of it has to explain how they creep into this little corner of the field. They win their chance of notice it appears not because they are members of an important independent class of the animal kingdom, but as a subordinate branch of the district's microscopic fauna. It is however a mistake to suppose that the carcino- logy of a county is wholly dependent for its interest on an extensive seaboard, or the presence of large lakes and broad rivers. Some crustaceans have in the course of ages, if theory may be trusted, forsaken that watery world in which alone their distant ancestors could breathe, and, whether theory can be trusted or not, as a matter of fact their existing generations live on land. Others there are among the fresh- water species as modest in their views as Cincinnatus, who preferred his little farm to a dictator's palace. They actually like a rivulet better than a river, and disdainful of spreading lakes make it a point of honour to swarm in small and shallow ponds. There are moreover a very great number which, though incapable of active life on land, can in the embryonic stage wait for water with admirable patience, choosing to be born only when there is liquid for them to live in. For the crustaceans of an inland county it is sufficient to distinguish two out of the three principal sections of the class, the Malacostraca and Entomostraca. All the crabs, lobsters, shrimps and other forms belonging to the former group are linked together by a community of structure much closer than at the first glance would be imagined. Leaving out of count the foremost piece to which the eyes belong and the hindmost piece called the telson, there are in the malacostracan body nineteen segments, and each segment has a pair of appendages assignable to it. That appendages are often missing, that segments coalesce, making two or more look like one, must be admitted. But the general state- ment is based on very substantial evidence. The appendages, for example, that are missing in one sex will be found in the other, or if 171
