ORGANS OF CIRCULATION. 



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the blood for distribution to all parts of the l)ody. The refuse 

 remaining in the alimentary canal (and which has never been a 

 part of the body proper) is finally voided throuLdi the anus as 

 Hastings ovfcBces. This process of " deftecation " must not be 

 confounded with that of excretion^ which will ]>e desciibed later. 



Circulatory System. The food, having been absorbed, is 

 distributed throughout the body by two devices. 



1. Coelomio Gircxdation. The cavity of the ca'lom is tilled 

 with a colorless fluid (' ' coelomic fluid ' ') which must be regarded as a 

 kind of lymph or blood. By the contractions of the body-wall, as 

 the worm crawls about, the cadomic fluid is driven back and forth 

 through all parts of the coelom, 

 through irregular openings in the 

 dissepiments. As the digested 

 food is absorbed from the stomach- 

 intestine a considerable part of it is 

 believed to pass into the coelomic 

 fluid, and is thus conveyed directly 

 to the organs which this fluid 

 bathes. The coelomic fluid is com- 

 posed of two constituents, viz., a 

 colorless fluid called the plasma, 

 and colorless isolated cells or coi'- 

 jpuscles which float in the plasma, 

 and are remarkable for the fact 

 that tliey undergo constant though 

 slow changes of form. In fact they 

 closely resemble certain kinds of 

 Ammhce, and we should certainly 

 consider them to be such if we 

 found them occurring free in stag- 

 nant water. We know, however, 

 that they live only in the plasiria, and have a connnon origin 

 with the other cells of the body ; hence we must regard them 

 not as individual animals, but as constituent cells of the eartli- 

 worm. The ccelomic fluid is in fact a kind of fisst/f' consisting 

 of isolated colorless cells floating in a fluid intercellular sul)stan('i'. 

 These free floating cells are probably the scavengers (j>/i(i(/<irt/f*s) 

 of the body, devouring and destroying waste matters. 8onio 



Fig. 25.— Phagocytes, from tlie cnp- 

 loinic fluid of the earthworm. .1, 

 af^glomeration of i»lia>:orytes, 

 surrounding a foreiRn body; /?, 

 sintrle uliaLTocyte, with vacuole^i. 

 (After MetschnikotT.) 



