94 THE BIOLOGY OF THE SEA-SHORE 



or to * right ' the body when placed in an abnormal pose. 

 There is a striking change in the tone of the muscles and 

 a great decrease in sensitiveness to touch and to pain." 



Among shore animals this phenomenon may readily be 

 observed in Carcinus moenas, Cancer pagurus, and other 

 Crustacea. On being seized in the hand the two species 

 just mentioned become perfectly rigid. There is a 

 characteristic difference in the manner of disposing the 

 appendages (thoracic). In Carcinus these are extended 

 almost at right angles to the body, the last joints alone being 

 somewhat bent, whereas in Cancer they are folded neatly 

 over the under-surface of the thorax as if to protect it. 



Fredericq (op. cit.) mentions Neritina sps., which creep 

 over the surface of submerged stones and when touched 

 quit their hold and fall to the bottom of the water. This 

 is analogous to the habits of certain terrestrial insects. 

 When a stone under which Porcellana platycheles is hiding 

 is upturned the crab will often " sham dead," and owing 

 to its frequent resemblance to its surroundings will then be 

 quite inconspicuous. 



One should guard against too readily assuming that this 

 habit of death-feigning is primarily or necessarily of an 

 adaptive nature. Issel (191 8) remarks that a state of hypnosis 

 due to loss of muscular tone is not necessarily induced by 

 the sight of another animal or by brusque contact with it. 

 Slight variations in the external medium are sufficient : an 

 inequality in the substratum, a difference of temperature 

 or of illumination ; indeed, slight stimuli are more effective 

 than strong ones. Recent experiments on Phasmids (stick- 

 insects) tend to show that in these animals " shamming dead " 

 is of the nature of a rhythmic phenomenon, i.e. it occurs 

 at definite intervals, and is not a direct response to any 

 external stimulus. Possibly the adaptation is secondary. 

 According to Bohn (191 1) the phenomena of death-feigning 

 are akin to those of " differential sensitivity " exhibited by 

 unicellular animals or tubicolous worms. 



Protective Resemblance. — Many shore animals, parti- 

 cularly those which are without skeletal protection, and are 



