ANIMAL CHLOROPHYLL 355 



5. ECHINODERMATA. 



It is generally accepted that the first phylogenetic appear- 

 ance of a vascular system is to be found among the echinoderms. 

 The animals of this phylum are provided with distinct organs 

 of circulation consisting of two radiating canal systems (haemal 

 and perihaemal), the most important of which arises from a ring 

 surrounding the oral end of the digestive tube. 



Although these vessels always contain a corpusculate fluid, 

 it is certain that they are incapable of either peristalsis or of 

 any other contractile manifestation. Also the sinus which 

 accompanies the madreporic canal, while usually looked upon 

 as a rudimentary heart, certainly performs no pumping func- 

 tion. Consequently serious doubt has arisen as to the correct- 

 ness of looking upon the haemal and perihaemal systems of 

 the echinoderms as true blood-vascular systems. 



The corpusculate fluid of the haemal and perihaemal vessels 

 is likewise found throughout the entire peritoneal cavity. 

 ' The corpuscles are nucleated cells, which exhibit amoeboid 

 movements ; and the fluid so obviously represents the blood 

 of higher animals, that I know not why the preposterous name 

 of " chylaqueous fluid " should have been invented for that 

 which is in no sense " chyle ", though, like the other fluids of 

 the living body, it contains a good deal of water ' (Huxley, 

 p. 480). 



(a) The Sea-urchin Tripneustes esculentus 



L e s k e . 



The red pigment cells are the most noticeable constituent 

 of the ])ody-fluid of this animal. With them are found non- 

 pigmented cells, vibratile cells which are supposed to facilitate 

 circulation, and, less frequently, yellow cells which are not 

 unlike Zooxanthellae.-^ The red cells are closely packed with 

 small granules ; when protruding its pseudopodia, the cell 

 first sends forth a thin, transparent lamella of hyalin ectoplasm, 



^ The most recent work on the body-fluid cells of sea-urchins is that of 

 Kollmann (1908). He recognizes five types of cell. 



