ANIMAL CHLOROPHYLL 383 



it is probable that their pigment is chlorophyll or a substance 

 closely allied (chlorophyll has been demonstrated in more than 

 twenty species of sponge), and there is evidence which indicates 

 that it, too, is obtained from external sources. 



3. The constituents from which actinians manufacture their 

 pigment are carried to the tissues by the gastrovascular fluid ; 

 it is likely that the constituents themselves are derived from the 

 chlorophyllous substances which enter as food ; thus they are 

 in a highly-organized state when they reach the tissues, making 

 the synthesis of the pigment less difficult. Certain of the acti- 

 nian pigments — aside from being derivatives of chlorophyll — 

 are closely related to haemoglobin (actiniohaematin). 



4. In certain fiatworms which are not coloured by algal 

 symbionts, the pigment is derived from food and is carried to 

 the tissues by the gastrovascular system. 



5. The pigment of the red cells of Tripneustes escu- 

 lent us, so numerous in the perivisceral fluid, is identical 

 with the pigment of the epidermis, and since it has been shown 

 by Geddes and others that the pigmented cells arise while in 

 circulation from yellow cells, direct evidence is thereby afforded 

 that the body pigment arises in the nutritive fluid. 



6. The red pigment, echinochrome, though probably not 

 respiratory (McClendon), nevertheless bears a close chemical 

 relationship to haemoglobin (Griffiths). 



7. Since there is every probability (in T. esculent us) 

 that the yellow cells from which the reds arise are chloro- 

 phylloid corpuscles, it seems clear that chlorophyll is capable 

 not only of giving rise to an animal pigment Init to a pigment 

 which is closely akin to haemoglobin (echinochrome breaks 

 down into haemochromogen, a reduction product of haemo- 

 globin). Blirgi's feeding experiments show that chlorophyll 

 facilitates the formation of haemoglobin in anaemic rabbits. 



8. The theory that haemoglobin is derived from chlorophyll 

 is further strengthened by the fact that in many echinoderms 

 there is present, simultaneously with haemoglobin and chloro- 

 phyll, a substance, haematoporphyrin, which is an intermediate 

 product chemically between chlorophyll and haemoglobin, 



