234 Prof. W. C. M'Intosh on the 
and occasionally between tide-marks, while a third is pale 
and more or less translucent. Moreover, the eggs of Nudi- 
branchs are generally conspicuous. 
The pelagic Gastropods also offer very varied coloration. 
Some are pale like Spiréali’s, others, darker like Limacina, 
show orange-pink like Clione, deep blue like Glaucus, purple 
like Janthina, or a glassy translucency like Carinaria and 
Pterotrachea. If, in the open ocean, translucency be a pro- 
tective attribute of such forms, it cannot be held that the 
tinted species conform to this view. Prof. Moseley, again, 
considered that Janthina and Glaucus (like Veledla) are 
coloured blue for protection, since they thus resemble oceanic 
water. There appears, however, to be no general feature in 
the pelagic stages of the group that would point out trans- 
lucency or a particular colour as the result of natural selection 
and of importance to the species. 
If translucency or a bluish tint are to be held as protective 
to oceanic forms, the pelagic cuttlefishes do not fulfil these 
conditions, for the play of colours, like those on “ shot silk,” 
occurs throughout the whole series. Moreover, though 
courtship is known to take place, and though the sexes offer 
certain external differences in structure, yet the colours are, 
as a rule, the same in both sexes ; so that, in these compara- 
tively intelligent and active Invertebrates, the long ages of 
Sexual Selection have effected no evident change in coloration, 
whatever may have been accomplished in other respects. 
The young forms on escaping from the egg are pelagic and 
have the same pigment-corpuscles as their parents, though, 
perhaps, they may be fewer in number. 
In the group of the Urochordates the translucent chains 
of Salpe have been cited as instances of protective coloration ; 
but the chains are readily seen in clear sea-water from the 
surface to the bottom, in several fathoms, probably 5 or 6. 
Moreover, the gulls readily strike the surface-forms and 
remove the nuclei containing the vital parts of the animal. 
Prof. Moseley thought that some Salye had a blue and others 
a brown nucleus for protection, but experience proves that 
both are equally liable to the attacks of gulls. ‘The trans- 
lucent Pyrosoma, again, 1s phosphorescent, and it cannot be 
supposed that it has this property to lure other forms to 
destruction, since it derives nourishment from minute plants 
and animals carried in currents of water. 
The Ascidians (Ascidia scabra) attached to the blades of the 
seaweeds in the Outer Hebrides, and to various structures in 
deeper water elsewhere, are brightly coloured ; yet this is not 
protective, as they are most conspicuous, nor can it always 
