118 The Outline of Science 



Shifts for a Living 



We get another glimpse of the intensity of the seashore 

 struggle for existence in the frequency of "shifts for a living," 

 adaptations of structure or of behaviour which meet frequently 

 recurrent vicissitudes. The starfish is often in the dilemma of 

 losing a limb or its life; by a reflex action it jettisons the captured 

 arm and escapes. And what is lost is gradually regrown. The 

 crab gets its leg broken past all mending; it casts off the leg 

 across a weak breakage plane near the base, and within a pre- 

 formed bandage which prevents bleeding a new leg is formed in 

 miniature. Such is the adaptive device more reflex than re- 

 flective which is called self-mutilation or autotomy. 



In another part of this book there is a discussion of camou- 

 flaging and protective resemblance; how abundantly these are 

 illustrated on the shore! But there are other "shifts for a living." 

 Some of the sand-hoppers and their relatives illustrate the puz- 

 zling phenomenon of "feigning death," becoming suddenly so 

 motionless that they escape the eyes of their enemies. Cuttle- 

 fishes, by discharging sepia from their ink-bags, are able to throw 

 dust in the eyes of their enemies. Some undisguised shore- 

 animals, e.g. crabs, are adepts in a hide-and-seek game; some 

 fishes, like the butterfish or gunnel, escape between stones where 

 there seemed no opening and are almost uncatchable in their slip- 

 periness. Subtlest of all, perhaps, is the habit some hermit-crabs 

 have of entering into mutually beneficial partnership (commen- 

 salism) with sea-anemones, which mask their bearers and also 

 serve as mounted batteries, getting transport as their reward and 

 likewise crumbs from the frequently spread table. But enough 

 lias been said to show that the shore-haunt exhibits an extraordi- 

 nary variety of shifts for a living. 



Parental Care on the Shore 



According to Darwin, the struggle for existence, as a big 

 fact in the economy of Animate Nature, includes not only compe- 



