ANIMAL CHLOROPHYLL 357 



cerning the origin of these pigment cells Geddes and Prouho 

 (1887) agree that the yellow cells ^ which are found in the body- 

 fluid give rise to the red cells ; they base their conclusion upon 

 the fact that at times many intermediate stages between yellow 

 and red cells are to be observed. In sea-urchins which had been 

 weakened on the preceding day by the loss of perivisceral 

 fluid, the writer also noticed intermediate stages between these 

 two corpuscles.^ The observations regarding the origin of 

 the red cells are of importance, since they give direct evidence 

 that the body-pigment arises in the blood-system. 

 Very little is known regarding the nature of the yellow cells 

 from which the red ones arise. It is quite possible that they 

 are chlorophyllous cells, as Geddes has suggested. But if this 

 is the case, we have before us a phenomenon of great impor- 

 tance, since it would afford direct proof that a chlorophyllous 

 substance gives rise to a haematin pigment. MacMunn (1883 c) 

 has found chlorophyll in the integument and certain tissues of 

 many invertebrates, including the echinoderms. In addition 

 he (1883 a) has described the red pigment of echinoderms as 

 being a definite chemical substance, which he has named 

 ' echinochrome '. This pigment was believed both by him 

 and by Griffiths to be respiratory in nature, but this has since 

 been denied by Saint-Hilaire (1896), and more recently by 

 McClendon (1912). Echinochrome has been analysed chemically 

 by Griffiths (1897) with the following result : 



Cio2 H99 N12 FeSa O12 



On boiling, the pigment is converted into haematoporphyrin 

 (p. 351) and haemochromogen, which shows that echinochrome 

 is related to haemoglobin ; the relationship, moreover, is 

 probably close, since it has in the molecule both Pe and S, 

 and also because it breaks down into haemochromogen, which 



^ Found most abundantly in Dorocidaris papillate, Arbacia, 

 and particularly in Spatangoidea. 



- In the study of the pigmented cells of A. atra (Fulton, 1921 h) 

 a similar phenomenon was observed ; in animals which previously had 

 been weakened by the loss of blood many intermediate stages between the 

 colourless cells and the pigmented corpuscles were observed. 



