166 THE DISTRIBUTION OF 
at the breeding-season, for the gravid female must come 
on shore to produce her young. 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 like plaice, dabs, turbot, 
skate, fishing frogs, &c., which haunt the sandy bottom, 
their shape fitting them for life here, to forms like cod 
and haddock, whose chief adaptation to littoral life 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 
littoral cod and haddock should have floating or 
pelagic eggs, and should in their early life haunt the 
surface, often seeking shelter within the bells of the 
pelagic jellyfish, while the herring, which in adult 
life 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 littoral forms. 
Many cuttles cower down on the sea-bottom waiting 
for their prey, or clamber over the rocks by the aid of 
