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 expan- 

 sion 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 



D 2 



