18 
H. N. MOSELEY. 
the skin being apparently immovable. Moreover, the struc¬ 
ture of the skin precludes the idea of its having a respiratory 
function. I believe that the transparent pelagic fish Plagusia 
will be found, like Leptocephalus, to be devoid of haemoglobin. 
I unfortunately did not test it with the spectroscope, but 
observed several living specimens to be devoid of red colour¬ 
ing under 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. 1 
Besides hannogloblin several others of the colouring 
matters here under consideration occur in curiously restricted 
regions in various animals. I have described in a former 
paper 3 the curious restriction of actiniochrome in specimens 
of 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 diffused generally in the tissues of some of the Coden- 
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 
Avhich 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, whilst 
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 
1 5' at' ilosole J> ‘ Nature,’ vol. v, January 4tli, 1872, p. 1S4. 
on “Actiniochrome,” ‘Quart. Journ. Mic. Science,’ Vol. 
XIII, 1873, p. 143. 
