38 jiVENINGS AT THE MICROSCOPE. 



ward along the three twists of the heart (ihe part bo 

 liind expanding immediately as the action passes on), 

 and the globules are forcibly expelled through the nar- 

 row but open extremities. Meanwhile, globules from 

 around the other end have rushed in as soon as that 

 part resumed its usual width, which in turn are driven 

 forward by a periodic repetition of the systole and 

 diastole. 



The globules, thus periodically driven forth from the 

 heart, now let us watch and see what becomes of them. 

 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 gen- 

 eral cavity of the body. 



Tlie greater number of globules pass immediately 

 from the heart throuo^h 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 sur- 

 faces of the sac and the inner surface of the bodv- 

 walls. 



But to return to the current which passes up the 

 right side : arriving at the upper angle oi the body, the 

 stream turns oft' 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, 



