UNIVERSITY OF CALIFORNIA PUBLICATIONS 



ZOOLOGY 



Vol. 1, No. 2 (pp. 105-1 14) April 30, 1903 



A CASK OF 



PHYSIOLOGICAL POLARIZATION 

 IN THE ASCIDIAN HEART 



BY 



FRANK W. BANCROFT and C. 0. ESTEELY 



INTRODUCTION. 



It is well known that, while in most animals the heart beats 

 continuously in one direction only, in the Ascidians its contrac- 

 tions normally reverse their direction at fairly regular intervals. 

 The earlier investigators, who studied the heart reversal chiefly in 

 the intact animal, mostly concluded either that the cause of the 

 reversal is the "necessity of the distribution of the arterial 

 blood to all the organs" (Roule, 1884, p. 151), or that it is the 

 increasing pressure that the heart has to labor against in forcing 

 the blood through vessels that cannot easily accommodate it 

 (Lahille, 1890, p. 292; Ritter, 1893, p. 7."i). 



Recently the problem of the reversal has been attacked from 

 a physiological point of view by Lingle (Loeb, 1900, pp. 28-29). 

 Professor Loeb has informed us orally that the species used in 

 these investigations was Molgula (Bostrichiobranchus) manhat- 

 tensis. Lingle found that if the heart be divided at the center 

 each half beats continuously from the end towards the cut; and 

 also that the automatic activity was confined to two small 

 regions near the ends, so that after these had been cut away 

 they continued beating, while the long part between them no 

 longer contracted in sea water. Professor Loeb has told us that 

 the central piece did not contract in a solution of pure sodium 



ZOOL.— 8 1 105 1 



^Qtuan Inst/; 



0CT21 ] 



