231 Prof. W. C. M'Intosli on the 



and occasionally between tide-marks, while a third is pale 

 and more or less translucent. Moreover, the eggs of Nudi- 

 branciis are generally conspicuous. 



The pelagic Gastropods also offer very varied coloration. 

 Some are pale like Spirialis, otliers, darker like Limacina, 

 show orange-pink like Clione, deep blue like Glaucus, purple 

 like JanthhiGf 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 Velella) 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 ^^g 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 SulpoB have been cited as instances of protective coloration ; 

 but the chains are readily seen in clear sea-water from the 

 suiface 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 Salpce had a blue and others 

 a brown nucleus tor protection, but experience proves that 

 both are equally liable to the attacks of gulls. The trans- 

 lucent Fyrosoma, again, is phosphorescent, and it cannot be 

 supposed that it has this propeity 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 



