100 HERBERT E. DURHAM. 
par se désagréger.” In the Spatangid where the effete pigment 
is more insoluble its porterage to the exterior is readily 
followed. 
The best known respiratory pigment is hemoglobin, and 
we know that it is constantly being destroyed and as constantly 
being manufactured ; moreover, that some of the products of its 
destruction are themselves pigmented. A priori, therefore, 
we should expect that further researches will show that the 
respiratory pigment (echinochrome) is always being destroyed 
and replaced by new; and it is probable that the pigment 
which is got rid of or deposited in the tissues is a product 
resulting from its disintegration; the process in the Spatangid 
then would form a fairly complete parallel to the above-quoted 
phenomenon, which occurs, e.g., in the frog, where respiratory 
hemoglobin gives rise to the dark effete “ melanin” (Gamgee, 
No. 30; J. H. List, No. 48; Latschenberger, No. 47; and 
Gaskell, No. 82) which is then got rid of through the skin, 
being of service as a colouring agent whilst en passage. 
Whereabouts in the Echinoderm does the pigmental change 
take place? Some authors (e.g. Hamann, No. 1) consider 
that the dorsal organ (chromatogen organ) is the seat of this 
change, others deny that it is—for instance, Prouho (11), on 
the ground that more effete pigment is found in the mesentery, 
&c., than in the dorsal organ. But the presence of inter- 
mediate forms of corpuscles show that some transformation 
occurs in the organ itself, though probably the change is not 
limited to the precincts of the organ.’ Its structure offers some 
facilities for the distribution and consequent non-accumulation 
of the pigment within it. If we could accept it as the place 
where these pigmentary and other waste substances are worked 
up, the organ could be closely compared to the pericardial 
gland of Lamellibranchs, &c. (Grobben, 38), and to the 
chloragogen cells of Chzetopods (Véjdovsky, 58) ; moreover it 
bears a very similar position to these structures as regards the 
possibility of actual ejection of the effete materials: with the 
1 Cf. Hisig, 27, ‘On Deposit of Concretions in other Organs than the 
Nephridia,’ 
