BLOOD. 35 



They do not appear to pass into any defined system of 

 vessels that we may call arteries, but to find their way 

 through the interstices of the various organs in the general 

 cavity of the body. 



The greater number of globules pass immediately from 

 the heart through a vessel into the short foot-stalk, where 

 they accumulate in a large reservoir ; but the rest pass up 

 along the side of the body, which (in the aspect in which 

 we are looking at it) is the right. As they proceed (by 

 jerks, of course, impelled by the contractions of the heart), 

 some find their way into the space between the breathing 

 surfaces, through narrow slits along the edges of the sac, 

 and wind along between the oval ciliary wheels, which we 

 will presently consider. Besides these, however, other 

 globules wind along between the outer surfaces of the sac 

 and the inner surface of the body- walls. 



But to return to the current which passes up the right 

 side : arriving at the upper angle of the body, the stream 

 turns off to the left abruptly, principally passing along a 

 fold or groove in the exterior of the breathing sac until it 

 reaches the left side, down which it passes, and along the 

 bottom, until it arrives at the entrance of the heart, and 

 rushes in to fill the vacuum produced by the expansion of 

 its walls after the periodic contraction. This is the perfect 

 circle ; but the minor streams that had forked off sideways 

 in the course, as those within the sac for example, find 

 their way to the entrance of the heart by shorter and more 

 irregular courses. 



One or two things connected with this circulatory system 

 are worthy of special notice. The first is, that its direc- 

 tion is not constant, but reversible. After we have watched 

 this course followed with regularity for perhaps a hundred 

 pulsations or so, all of a sudden the heart ceases to beat, 

 and all the globules rest in their circling course, that we 

 had supposed incessant. Strange to behold, after a pause 

 of two or three seconds, the pulsation' begins again, but at 



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