18 n. N. MOSELEY. 



the skill being ajjparently immovable. Moreover, the struc- 

 ture of the skin prechides the idea of its having a respiratory 

 function. I believe that the transparent pelagic fish Plagusia 

 will be founds like Leptocephalus^ to be devoid of haemoglobin. 

 I unfortunately did not test it Avith the spectroscope, but 

 observed several living specimens to be devoid of red colour- 

 ing xmder the microscope. I examined many Planarians for 

 haemoglobin, but did not find it in any, although it occurs 

 in a parasitic species which I found at Suez in 1872.^ 



Besides heemogloblin several others of the colouring 

 matters here under consideration occur in curiously restricted 

 regions in various animals. I have described in a former 

 paper" the curious restriction of actiniochrome in specimens 

 oi Bunodes crassicornis, which are decolorised by the action 

 of muddy tidal water, to the gonidial tubercles of the animal. 

 Turacin is restricted to certain feathers and certain parts 

 of feathers only, and in Labricthys the green pigment dis- 

 covered by Mr. G. Francis is restricted to certain stripes on 

 the body. Polyperythrin was found, as already described, 

 to be diff'used. generally in the tissues of some of the Coelen- 

 terates in which it occurs, whilst in others it is restricted to 

 certain superficial stripes, and in one Actinia to the surfaces 

 of the mesenteries in the interior of the animal only. In 

 different specimens of the same species, Flabellum variabile, in 

 which species it is often present in abundance, it is sometimes 

 entirely absent, sometimes tinges the calcareous skeleton, and 

 sometimes does not. 



Pentacrinin and Antedonin seem to be widely diffused in 

 immense quantities through the tissues of the crinoids in 

 which they occur; and Echinoderms generally seem to be 

 characterised by the presence of evenly diffused, abundant and 

 readily soluble pigments. 



Those colouring matters which, like those at present under 

 consideration, absorb certain isolated areas of the visible 

 spectrum, must be considered as more complex as pigments 

 than those which merely absorb^more or less of the ends of 

 the spectrum, since in the latter case the sensation of result- 

 ing colour is produced by the action on the eye of an evenly 

 graduated range of light of various refrangibilities, M'hilst 

 in the former the scale of colours is interrupted at variously 

 placed intervals of darkness, and a more complex mixture of 

 residual colours ensues. By the human eye the finer com- 

 plexities of colour are not distinguished, and although some 



' H. N, Moseley, 'Nature,' vol. v, Jauuary 4th, 1872, p. 184. 

 ' H. N. M., on " Actiuioclirome," ' Quart. Journ. Mic. Science,' Vol. 

 XIII, 1873, p. 143. 



