28 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



might see a reversal of the heart-beat. Nature has 

 made this experiment for us on a large scale in the 

 Ascidian's heart (Fig. 6). 



The latter has the peculiarity that the waves of 



contraction do not 

 spread out con- 

 stantly in one di- 

 rection, as in the 

 hearts of other an- 



_ imals, but perist- 



altic and antiperi- 



IMG. 6. DIAGRAM OF THE ASCIDIAN HEART. 



staltic waves of 



In the Ascidian heart, contractions occur for a time 



in the direction from a to b, and then from b to Contraction alter- 



a. If the heart be cut open at c, the left half nate in it If for 

 contracts only in the direction from a to c, the , . , 



right half only in the direction from bloc. example, it has 



contracted five 



hundred times in succession from left to right, sending 

 the blood to the right, this activity is followed by per- 

 haps three hundred pulsations from right to left, 

 which cause the blood to flow through the blood- 

 vessels in the opposite direction. These contractions 

 are followed again by a large number of pulsations 

 from left to right, etc. Mr. Lingle made the follow- 

 ing experiments on the Ascidian's heart at Wood's 

 Holl in 1892. If a b (Fig. 6) be an Ascidian's heart 

 and it be divided at c, both pieces, a c, and b c, con- 

 tract uninterruptedly in a constant direction, the 

 former in the direction from a to c, and the latter in 

 the direction from b to c. Mr. Lingle found, further- 

 more, that the source of the automatic activity is 



