ANIMAL CHLOROPHYLL 353 



from which it elaborates its pigment ; the components, in 

 addition, are probably highly-organized substances. The 

 gastrovascular fluid derives these pigment-making substances 

 from the chlorophylls which enter as food. The pigment, 

 therefore, in addition to bearing a close relationship to haemo- 

 globin, is probably itself derived from chlorophyll. This 

 applies to MacMunn's actiniohaematin ; and it will also be 

 recalled that Elmhirst and Sharpe (1920) have shown that 

 the non-haematin pigment of A. equina releases oxygen 

 as a result of photosynthesis, which likewise suggests an 

 intimate relation to chlorophyll. 



4. Platyhelminthbs-. 



Huxley (1877, p. 57), writing of the digestive cavity in the 

 Coelenterata, remarked that the ' fluid which it contains 

 represents blood '. Concerning the next higher group he states : 

 ' In the Turbellaria, Trematoda, and Cestoidea, the lacunae 

 of the mesoderm and the interstitial fluid of its tissues are the 

 only representatives of a blood-vascular system.' The observa- 

 tion of Huxley is interesting, but it must be recalled that 

 the mesodermal lacunae represent merely the morphological 

 homologue of the blood-system ; ^ the functional precursor 

 of the vascular system, as in the coelenterates, is to be found 

 in the gastrovascular cavity. 



Pigmentation is common among the flat worms ; many 

 of the marine polyclads, in particular, are distinguished by 

 a brilliant coloration. The only investigations concerning the 

 pigment of the animals belonging to this class with which the 

 writer is acquainted are those of Gamble and Keeble, and Crozier. 

 The latter author (Crozier, 1917) has shown that the polyclads 



^ Though the supply of pigment-forming substances is undoubtedly 

 given by the gastrovascular system, it is interesting to note that among 

 the Rhadocoele Turbellaria the parenchyma (in which the lacunae 

 are formed) is the seat of the body-pigment (Parker and Haswell, vol. i, 

 p. 265). This seems to be the first instance in which the function of provid- 

 ing pigment has been taken over by the morphological fundament of the 

 future blood-system. 



