CHAP. IV Shifts for a Living 65 



the shrimp (Crangon), and the prawn (Palcemori). In crabs 

 and in the spiny lobster the surrender of a limb is effected 

 by the forcible contraction of the basal muscles, and the 

 line of rupture is through the second-lowest joint. Fr^d^- 

 ricq's researches seem to prove conclusively that the sur- 

 render is a reflex and unconscious act, but its protective 

 value is not less great. The chances are in favour of the 

 crab escaping, the residue of muscle prevents haemorrhage 

 from the stump, and in the course of time the lost limb is 

 replaced by a new growth. The crab does not know what 

 it is doing, but it unconsciously illustrates that it is better 

 that one member should perish than that the whole life 

 should be lost. 



Not a fev? insects readily surrender their legs, but these 

 are not replaced. Spiders are captured if the legs are fixed 

 without irritating the nerves, for that is an essential con- 

 dition of the reflex amputation. In regard to hzards, also, 

 it has been shown that a reflex nervous excitement, and not 

 mere brittleness, is the condition of surrender. Here, how- 

 ever, the lost tail may be replaced. Among Mollusca a 

 surrender of parts has been recorded of Harpa ventricosa, 

 Doris cruenta, Stenopus, some species of Helix, the razor- 

 shell Solen ; while it is well known that male cuttle-fishes 

 sometimes part with one of their arms for special sexual 

 purposes. A great many " worms " break very easily, and 

 the severed parts are sometimes able to regrow the whole 

 organism. 



Among the Echinoderms the tendency to disrupt is exhi- 

 bited to an extraordinary degree. Thus Professor Preyer has 

 shown that the seven -rayed starfish (Asterias tenuispina) 

 surrenders its arms with great readiness, often giving off 

 three or four at a time. But each ray may reproduce an 

 entire starfish. Professor Edward Forbes tells how a speci- 

 men of Luidia, which he had dredged, was disappearing 

 over the side of the boat when he caught it by one of its 

 arms; it surrendered the arm and escaped, giving "a wink 

 of derision " with one of its eyes. Brittle-stars (Ophiuroids) 

 of many kinds are true to their popular name, and the 

 Crinoids are not less disruptive. Not only are the arms 



r 



