THE LYMPH AND LYMPHATIC SYSTEM 339 



(proportionately) more liquid. The liquid is "lymph," 

 like that of the Vertebrate, and has numerous proto- 

 plasmic cells floating in it. There is comparatively little 

 connective tissue in the earth-worm. The ccelom is free 

 and unblocked the great viscera lie in it. There are 

 some delicate, transparent bands of connective tissue, but 

 not much nor bulky. The wall of the coelom itself is 

 lined with connective tissue, and if that tissue grew greatly 

 in bulk, and bound all the organs and muscles together, it 

 would reduce the large cavity, filling it up with spongy 

 tissue in the small interstices of which there would 

 be lymph. And so we should get a lymph system 

 resembling that of Vertebrates, instead of one large 

 chamber. 



But what about the opening of the lymphatics into 

 the blood-vessels ? This is one of the interesting differ- 

 ences between the earth-worm and the Vertebrate. The 

 earthworm and many marine worms have a beautiful 

 system of vessels, containing a bright red blood, and 

 forming true capillaries, connecting arteries and veins. 

 The heart is a long, rhythmically beating tube, extending 

 along the whole length of the animal just above the 

 intestine. There is no opening into it of the lymph- 

 cavity. It is purely a respiratory blood-system, pump- 

 ing its fluid, coloured red by oxygen-seizing haemoglobin 

 into every part of the body. It passes along the fine 

 capillaries of the skin, where it seizes oxygen from the 

 outside air or water and carries it to all the tissues. 

 The fact is that the red respiratory element of the blood 

 which we call the " haema " or haemal portion (the 

 Greek word for red blood is alfjui) is here kept separate 

 from the nourishing and elaborating element, the lymph 

 or lymphatic portion. So that we should, to be explicit, 

 describe the blood of a vertebrate as " haemolymph," a 



