Coloration of Marine Animals. 231 
and the enormous powers of reproduction, suffice in some 
cases for safety. ‘Those which perforate rocks, wood, and 
other media are, as a rule, white, yet the date-shell (Litho- 
domus) has dark brown valves, whilst Modiolarda in the tests 
of Ascidians and in sponges is feebly tinted. The species 
which burrow in sand have diverse and often bright tints, 
such as Psammobia and Tellina, dull brown, as in Cyprina, 
or pale, ike the cockle and Thractia. Littoral forms are 
likewise varied. ‘The mussel is dark blue or purplish blue on 
mud or rock ; Galeomma with its outspread valves on the 
under surfaces of stones is pure white, Arca in the chinks of 
rocks is dull grey, and Lima hians has brilliant orange fringes, 
but the animal makes a nest. ‘The beds of sedentary dull 
greyish oysters and the brownish-black horse-mussels in the 
adjoining area under water are in contrast with the more 
brightly tinted and free scallops in similar regions, 
‘There is endless variety under the same circumstances, 
but no ceitainty as to protective or warning coloration or 
sexual changes in the valves of marine forms. 
It is interesting that pelagic young mussels and the slightly 
older forms which settle on zoophytes in myriads are differ- 
ently tinted from the adults. ‘The latter (young mussels) 
especially harmonize with their surroundings. ‘The pelagic 
young of marine lamellibranchs (after the formation of the 
shells), indeed, seem to approach each other more or less 
closely. 
The parasitic bivalves, like Montacuta substriata on Spatan- 
gus purpureus, are in harmony with their surroundings, 
though as regards coloration they are pale and more or less 
transparent. 
Coloration in the univalves (Gastropoda) has no apparent 
relation to their acceptability to forms which prey on them, 
and therefore has no protective or warning functions. All 
the available smaller forms—whatever their colour may be— 
are equally palatable to the haddock, which, as Kdward 
Forbes said, is a great conchologist. In their pelagic stages, 
it is true, they are less brightly tinted, and thus may be held 
to be protectively coloured; but other young forms, which 
are not pelagic, are of similar pale or neutral hues, so that 
there is room for doubt. ‘The question may well be asked, 
Are the bold bluish iridescent streaks of Helcion pellucidum 
equally protective or warning in the young on the dark blades 
of the tangles in the rock-pools, and on the adults hidden 
under the hard roots of the same seaweed ? 
Protective coloration in the Gastropods is exhibited by 
Ovula patula on Gorgonia verrucosa (Poulton) and Ovulum 
