108 University of California Publications. [zoology. 



We have seen that Lingle and Schultze agree that if a part 

 of a tunicate heart be physiologically connected with but one of 

 its ends, the contractions continue uninterruptedly from that 

 end. This result we obtained in most cases, though occasional 

 exceptions were encountered. Now the fact that we wish par- 

 ticularly to emphasize, and to the consideration of which this 

 paper is devoted, is that not only does the direction of the con- 

 tractions remain fixed while a part of the heart is connected with 

 only one cf its ends ' tint that in some way a clam:/: is zffzsted it, 

 the heart tissue so that the direction of the contractions still 

 remains fixed after the part has been isolated from the. end which 

 was instrumental in producing the fixation. That is, we may say 

 that the heart tissue has become physiologically polarized by 

 being left in contact for a while with only one end of the la-art. 



Experiments directed merely to determining whether such a 

 polarization is a fact consisted first in leaving a part of the la-art 

 connected with only one of the ends for a while. It was then 

 isolated from this end, the direction of the contractions noted, 

 and finally frequently divided into still smaller pieces, and the 

 direction of the contraction in each recorded. The character of the 

 evidence is best made clear by reference to a typical experiment: 



Experiment 39a. — 



10:37 — Visceral! end of la-art removed. The contractions are 

 ab-branchial.t 



10:44 — Pulsations have continued in the same direction. 

 Branchialt end removed. Pulsations in the long cen- 

 tral loop of the heart are still ab-branchial. 



10:. 'A — Visceral side of the loop cut in half. 



10:58 — Pulsations in both the pieces thus formed are ab- 

 branchial. 



' It should be stated that in all of these experiments the two ends behaved the 

 same. We could not see that it made any difference which end was cut away first. 



tin Clona one end. which is attached to the viscera, is called the visceral, and 

 the other, which connects with the branchial sac, is called the branchial end. Con- 

 tractions passing in the direction from the branchial towards the visceral end are 

 called ah-branchial, those passing in the opposite direction ab-visceral. This 

 nomenclature is that of Schultze slightly modified. 



