166 THE DISTRIBUTION OF 



at the breeding-season, for the gravid female must come 

 on shore to produce her yoimg. For this purpose she 

 visits the shores of low islands, where she may be found 

 coiled up among the rocks. 



The fact that amphibians have unprotected skins, 

 through which salt can pass very easily, makes them 

 intolerant of its presence, and we have thus no marine 

 amphibia. 



Littoral fishes are many, and range from forms like 

 the lumpsucker, the gobies, the sea-horses, the pipefish, 

 and so forth, which inhabit rocky pools within or close 

 to tide marks, through forms hke plaice, dabs, turbot, 

 skate, fishing frogs, &c., which haunt the sandy bottom, 

 their shape fitting them for hfe here, to forms like cod 

 and haddock, whose chief adaptation to littoral Hfe is 

 that they are ground feeders, depending upon animals 

 like hermit crabs, marine worms, shellfish, &c., which 

 only occur on the bottom. 



It is a curious illustration of what has been already 

 said as to the tendency to change from the pelagic to 

 the littoral habitat during the life-history, that the 

 httoral cod and haddock should have floating or 

 pelagic eggs, and should in their early life haunt the 

 surface, often seeking shelter within the beUs of the 

 pelagic jellyfish, while the herring, which in adult 

 hfe is a pelagic fish, feeding on free-swimming Crus- 

 tacea, has heavy or demersal eggs, which sink to the 

 bottom. 



The tunicates or sea-squirts mostly attach them- 

 selves to the sea-bottom, but have pelagic free-swim- 

 ming larvae. 



Of the molluscs a vast number are httoral forms. 

 Many cuttles cower down on the sea-bottom waiting 

 for their prey, or clamber over the rocks by the aid of 



