CRUSTACEANS 



Malacostraca this is the only representative likely to be found living, in 

 a wild or natural state, in the county. In all epochs of human history 

 this and its kindred species have probably been consumed in large 

 quantities for food. In the present epoch they are consumed in large 

 quantities for education. Their fitness for this purpose should not be 

 disregarded. Everything nowadays has to submit to analysis or dissec- 

 tion or both, water and milk, stars and ether, history and law, plants 

 and animals. Among the latter enthusiastic students make their choice, 

 some taking delight in the viscera of a kitten or the brains of a baboon, 

 others preferring the minute anatomy of a slow-worm or a slug. Very 

 likely all these subjects, according to taste or whatever the appreciative 

 sense may be, are delectable handling and alluring to look at. But for 

 unsophisticated persons, not yet prejudiced in favour of a snail or a 

 cuttle or a sea-sausage, one can honestly commend the class of Crustacea 

 as a basis and beginning of anatomical practice. Within that class the 

 river crayfish supplies the very model of a handy specimen, not clumsy 

 like a lobster, not inconveniently small like a shrimp, and withal so de- 

 cent and decorous, internally and externally so free from anything to 

 cause disgust, that the student may with satisfaction begin his study by 

 eating a large part of his lesson book. For even when the meat or 

 muscular part has been consumed the external skeleton remains, not un- 

 instructive. All through the wonderfully diversified orders and sub- 

 orders of the Malacostraca the fundamental character of that skeleton is 

 found persistent. In some great sections of the group the species have 

 their eyes set on movable stalks. In other great sections they have 

 them seated immovably in the head. But interlacing characters make 

 it difficult to draw a sharp line between these two assemblages. Apart 

 from the eyes there are normally nineteen pairs of appendages in all the 

 Malacostraca, each pair having theoretically a segment of the body to 

 which it is attached, while the body ends in a segment which has no dis- 

 tinct appendages. The eyes are followed by two pairs of antennas or 

 feelers, a pair of mandibles usually stout or sharp for biting or piercing, 

 two pairs of maxillae thin and flat, and then a pair of jaws called maxilli- 

 peds because they are sometimes foot-like. After these come either two 

 more pairs of maxillipeds and five pairs of legs, or else a complete series 

 of legs in seven pairs. But the so-called legs are seldom all of them 

 fitted for walking. The terminal portion of the animal known as the 

 tail, the abdomen, the pleon or swimming part, carries six pairs of ap- 

 pendages, some of them called pleopods or swimming feet and some 

 uropods or tail-feet, but under whatever names they pass subject to much 

 diversity in form and function. From the Decapoda or ten-footed divi- 

 sion Huxley selected ' the crayfish ' as the subject of a lucid and concise 

 zoological treatise. His explanations however are not limited to a page 

 or a paragraph, but expanded into a volume, and in its chapters those who 

 live where crayfishes live will amply learn what excellent opportunities 

 for mental improvement that companionship affords them. 



For specimens of Buckinghamshire sessile-eyed crustaceans I am 



III 



