A HISTORY OF HERTFORDSHIRE 



for the marine lobster, and the specific name jluviatilis for a kindred 

 species of crayfish found in various parts of the European continent, but 

 not in England. 



Although the common lobster and the common shrimp are easy to 

 obtain inland, as a scientific object of investigation the crayfish has an 

 advantage over both by hitting the happy mean between over large and 

 over small. But all three are convenient to handle, and may be used 

 together to throw light upon the fascinations of comparative anatomy. 

 On the other hand, for the observing of manners and customs, of the 

 arts and crafts, the dwelling-places and the breeding-habits of the living 

 creature in a word, for all that concerns the now popular study of 

 biology the river crayfish is of unique importance to Midland carcino- 

 logists. In a general way almost every one is willing to admit, with or 

 without reserve, the philosophical axiom that nature makes nothing in 

 vain. Yet scarcely to any one, except a thoughtful expert, will it readily 

 occur to suppose that there can be any special philosophy in the joints 

 of the leg or the body-segments of a Potamobius, a creature made to be 

 eaten, an unconsidered trifle, the garnish of a dish ! It is not that there 

 has been any such want of appreciation on the part of naturalists, for 

 they at intervals for centuries past have studied this genus with almost 

 loving care. Already in the middle of the sixteenth century observation 

 and experiment were brought to bear upon it. Like man himself, it is 

 tolerably omnivorous. Like so many other crustaceans, it is in part a 

 scavenger. Vegetable food is welcome, but perhaps animal food and 

 offal even more so. Thus the old author Gesner states that if the car- 

 case of a horse or dog or any other animal be submerged, the crayfishes 

 presently like vultures gather about it in swarms, not to quit till every 

 morsel of flesh has been eaten off. He tells also of a man who could 

 not help thinking that these swarms must be generated from the horse's 

 body, like the bees of Aristasus from the corrupting entrails of a 

 slaughtered bull. But when this person had from time to time thrown 

 dead horses into the water, the result of his experiments weaned him 

 from his poetical fancy. 1 The several illustrious men who between 

 Gesner's time and Huxley's have studied the crayfish in various aspects 

 might be thought to have exhausted the subject. But the comparatively 

 recent work of Dr. Theodor List on the motor apparatus of the Arthropoda 

 shows that this is by no means the case. Dr. List tracks the crayfish to 

 its favourite brooks, observes its preference for proximity to a bridge, 

 where it may find places of ambush and shelter from the odious daylight. 

 He descries it lurking among the stones in the bed of the rivulet, with 

 only its large claws emergent, in readiness to snap the passing prey. ' If 

 you attempt to catch it, you become aware that the abdomen, which it 

 flexes several times in rapid succession, is a capital locomotive apparatus. 

 Otherwise by day it is a very lazy customer. But as soon as darkness 

 has set in it leaves its hiding-place and goes on the prowl. With the 

 great claws stretched in advance, the large antennae feeling about in all 



1 Gesner, Hiitorue Animalium, liber iv., 1558 (ed. 1604, p. 105). 



182 



