Page:VCH Worcestershire 1.djvu/164

 CRUSTACEANS Scientific literature appears to contain scarcely any specific records relating to Crustacea in Worcestershire. Nevertheless, with a view to the growing interest in questions of distribution and in the details of every local fauna, it may not be superfluous briefly to indicate what groups of Crustacea will beyond question be found represented within the limits of the county, and some of the species the search for which will more or less certainly be rewarded with success. The zoological class with which we are concerned is commonly divided into two principal branches, the Malacostraca and the Entomos- traca. The former of these two has attained a position by far the higher in what may be called the scale of intellectual development, although by parasitic habits a few of its members have fallen back into a state of disgraceful degradation. Many persons are much surprised when first they hear that the unfavoured woodlouse is not only a crustacean, but be- longs to the aristocratic section of the class, and is distinguished even in that section by having had the energy and enterprise to forsake an aquatic existence for life upon land. The tremendous character of the change from water-breathing to breathing air may be realized by any one who attempts to reverse the process. The woodlouse is a terrestrial isopod. An isopod is a sessile-eyed crustacean of the kind which as a rule has the breathing apparatus in the appendages of the pleon or tail-part. Of the land isopods some go wherever man goes ; some have their special pro- vinces, districts, or isolated localities. England, without being very richly provided, has several genera and species, and some of these are so generally distributed over the country that their occurrence in this county, as in others, may be affirmed with the utmost confidence. Such are Oniscus asellus, Linn., ' very common throughout England, Scotland and Ireland under decaying vegetable and animal matter, not only in damp, but in the dryest localities ' ; ^ Porcellio scaber, Latreille, of which Bate and Westwood say that they have ' found it partial to growing vegetables, and it appears to possess a strong partiality for nearly ripe wall-fruit,' this dainty animal ' being widely distributed throughout England and Ireland';^ Armadillidium vulgare (Latreille), one of the ' pill-millepedes,' not to be confounded with the larger and less common G/omeris margwata, not a crustacean but a myriapod, with which it shares the habit of rolling itself up into a complete ball. Bate and Westwood expressly state that the Armadillidium is very abundant in the midland 1 Bate and Westwood, British Sessile-eyed Crusttnen, vol. ii. p. 471. 2 /,(,,■ (-,7 p ^yj, 126