Page:VCH Kent 1.djvu/288

 A HISTORY OF KENT this bountiful supply. Inquiries with a view to restrictive legislation have led to many valuable reports, those of recent years by Wilson, Meek, Cunningham and Williamson usefully combining scientific with economic conclusions. Only one or two points out of many can be considered here. The process called ecdysis or exuviation is repeated probably several times in the life of every crustacean that reaches maturity. Many a schoolboy, preparing for a swim, instead of sedately taking off his garments one by one, will slip out of them all at one cast. A crab with the growing pains improves upon this. It slips out of its skin. It comes so clean and clear away from the skin of its teeth and the teeth of its skin that the slough is a complete model of the animal with carapace, limbs, jaws, feathered hairs, delicate spines, or whatever else may be the appropriate furniture. Having become too stout for its unyielding harness the crab bursts it, obviously for the sake of getting a chance to expand in a new and still flexible vest. But such of the Decapoda as have inflated claws, strongly encrusted and narrow at the joints, can find no easy task in withdrawing their arms from these natural sleeves. The procedure which they have inherited and cannot dispense with is no longer very well suited to the accoutrement with which in process of time they have become equipped. But besides being essential to growth, the casting of the shell is also of service in the pairing of crabs. It does not occur simultaneously in the two sexes. The male Cancer pagurus is still securely armoured while his consort is in the soft helpless state which follows exuviation, and under these circumstances is repeatedly found keeping watch and ward over her. Some naturalists, observing the husbands in this apparently chivalrous attitude, looked upon it as probably ' a pretty trait of cancerine character, and one not unworthy of their acute instinct and sagacity in other respects.' ' There is however a somewhat less sentimental explanation available. There is reason to think that only while the skin of his partner is still pliable can the male find the auspicious time for intro- ducing into the spermatheca the fertilizing elements.'' Between the two sexes there are several differential characters. By one of them, according to Dr. Williamson, ' it is possible to distinguish the sex of a crab when it is little more than a quarter of an inch in breadth.'^ This difference lies in the circumstance that the infolded abdomen or pleon of the female has four pairs of swimmerets, whereas the first and second paired appendages of the male pleon are modified into organs for conveying the spermatophores into the spermatheca. While both sexes are still small, the narrow pleon of the male is contrasted witb the broad one of the female, and later on the male is further distinguished by his more mas- sive claws and by having the crenulated edge of his carapace broader and somewhat upturned. That the genital openings belong to the ultimate thoracic segment in the male but to the antepenultimate in the 1 White, Popular History of British Crustacea, p. 39 (1857), quotation from Gosse. ' Fishery Board for Scotland, l8iA Annual Report, pt. 3, 82. 3 Loc. cit. p. 99. 238