BLOOD 49 



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 per- 

 fect circle ; but the minor streams that had forked off side- 

 wise 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 sys- 

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

 rection 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 be- 

 hold, after a pause of two or three seconds, the pulsation 

 begins again, but at the opposite end of the heart, and 



r-SclENCE 3 



