226 Prof. W. C. M‘Iutosh on the 
be said of the purple or orange hue of S. endeca from deep 
water and of Cribrella sanguinolenta between tide-marks. 
The sand-stars (e. g. Ophiura lacertosa) are often tinted of a 
hue resembling their surroundings, yet they and the more 
brightly tinted forms are common in the stomachs of fishes 
and are eagerly devoured by gulls when stranded on the 
beach. 
The common sea-urchins of our own shores are often con- 
spicuous on the tangles at extreme low water, and their tints 
are neither protective nor warning as regards man and certain 
fishes. Though some species (e. g. Strongylocentrotus lividus) 
show sexual differences, the male being darker and the female 
of a violet tint more inclined to red, Sexual Selection need 
scarcely be considered. The burrowing habit of the species 
just mentioned would seem to indicate that its colour was 
neither protective nor warning. ‘The colours and habits of 
the heart-urchins give the same lessons. Amongst others 
the green-pea urchin is a favourite food of the haddock. 
‘The brown and purple hues of the sea-cucumbers may in 
some way subserve protection amongst the dark masses of the 
tangles, yet both they and the transparent forms are found in 
the stomachs of fishes. In the purple forms in the deep sea 
Prof. Moseley is of opinion that the colouring is useless, 
‘and is merely due to the persistence of colouring developed 
originally in shallow-water ancestors.” But there may be 
other explanations which are less theoretical, especially as 
the same purple colour is found in a feather- star in shallow 
water in the tropics and in a sea-cucumber in 1955 fathoms in 
the antarctic sea. 
The transparent Holothurians and the Synaptide are often 
almost colourless, so that the arguments in connexion with 
coloration do not fit. 
No group is more beautiful or more varied in coloration 
than the marine Annelids, and no group of Invertebrates 
offers a better field for the manifestations of protective resem- 
blance, for the display of warning coloration, and, since the 
sexes in the majority are separate, for the operations of Sexual 
Selection. Yet some of the most brilliantly tinted, like the 
sea-mouse, frequent muddy sand or mud, where the metallic 
lustre of their resplendent bristles would only betray them ; 
and the same may be said of some of the most conspicuously 
coloured Hesionida, e.g. Ophiodromus. It is true the bright 
colours and iridescence of many are hidden within tubes, but 
this would rather point to coloration in these cases being inde- 
pendent of protection. Even in forms that dwell in sand, 
like Nephthys, Ophelia, and Mugelona, the iridescent pearly 
