IV 



SHIFTS FOR A LIVING 



67 



moves." In further illustration of masking we may cite 

 Dromia vulgar is, often covered with sponge ; Dromia 

 excavata, with compound ascidians ; the Amphipod 

 Atylus, with seaweed ; while a species of Dorippe carries 

 about a bivalve shell, or even a leaf, as a shield, and 

 another crab cuts off the tunic of a sea-squirt and hitches 

 it on its own shoulders. 



Sometimes this masking serves as a warning or deter- 

 rent ; witness that hermit-crab (Pagurus cuanensis) whose 

 stolen shell is surrounded by a bright orange sponge 

 (Suberites domuncula). As this sponge is full of flinty 

 needles, has a strong odour and a disagreeable taste, we 

 do not wonder that fishes reject it (as Prof. Garstang has 

 shown), nor can w r e doubt that the hermit-crab trades on 

 the reputation of its associate. In other cases the mask- 

 ing will aid in concealment and favour attack. To the 

 associations of crabs and sea-anemones we shall after- 

 wards refer. 



11. Combination of Advantageous Qualities. Prof. 

 Poulton describes, in illustration of the combination of 

 many methods of defence, 

 the case of the larva of the 

 puss-moth (Cerura vinula). 

 It resembles the leaves of 

 the poplar and willow on 

 which it lives. When dis- 

 turbed it assumes a terrify- 

 ing attitude, mimetic of a 

 Vertebrate appearance ! 

 The effect is heightened by 

 the protrusion of two pink 

 whips from the terminal 

 prongs of the body, and 

 finally the creature defends 

 itself by squirting formic 



acid. Yet in spite of all this power of defence, the 

 larva often falls a victim to ichneumon-flies. These 

 manage to lay their eggs within the caterpillar, which 

 by and by succumbs to the voracity of the hatched 

 ichneumon grubs. Prof. Poulton believes that the puss- 



FIG. 18. " TERRIFYING ATTI- 

 TUDE " OF THE CATERPILLAR 

 OF Cerura vinula. 



(From Chambers's Encyclop. ; 

 after Poulton.) 



