106 University of California Publications. [zoology. 



chloride. In commenting upon these results Loeb (1900, p. 29) 

 says that they prove that the reversal is "determined by each of 

 the two ends getting the upper hand alternately, and forcing the 

 other to act in its rhythm for a while." This explanation was 

 tested by the members of Professor Loeb's elass in physiology at 

 Wood's Hole, who found that towards the end of a series of 

 contractions passing from one end, a, the beats become slower, 

 or stop altogether. During this pause the other end, l>, "suc- 

 eeeds iii sending out a wave of contraction which reaches a 

 before it has a chance to send out a wave of its own." Occa- 

 sionally both ends contract at the same time, lint the one which 

 is about to stop delays in sending out its next contraction, and 

 thus the beat from the end just beginning to contract can 

 traverse the whole heart. Schnltze (1901) in his study of the 

 heart of Salpa came to the same conclusion as Loeb concerning 

 the cause of the reversal, and confirmed most of the results of 

 Lingle and Loeb's students. He found, in addition, that even 

 when one end of the heart had been cut away, the rest of it 

 which continued beating in one direction, regularly gave rise to 

 alternating series of slower and faster contractions.'' 1 The slow 

 series, he thought, corresponded to the time when, in the intact 

 heart, the contractions would have been coming from the end 

 which had been removed. He also discovered that a constant 

 direction of contraction could be maintained by electrical stimu- 

 lation of either end of the heart. This stimulus so increased the 

 rate of contraction that the unstimulated end could not get con- 

 trol of the heart. In both Salpa and Ciona Schultze found that 

 isolated pieces from the center of the heart would contract in sea 

 water if they were left- there long enough. 



Neither Schultze nor any of the previous investigators of the 

 subject have found ganglion cells in the Tunicate heart. Hunter 

 (1902), however, has found in Molgula manhattensis a small 

 collection of ganglion cells at both ends of the heart, where the 

 contractions originate, and in a later paper (1903) has given 



*We observed rtn- same phenomenon in Ciona hearts from which "in- end had 

 been removed. In such hearts series of normal and much slower contractions 

 alternated. In some cases the heart would contract normally I'm- n while, then stop 

 entirely for a time that about corresponded t" the duration of rhe series of slow 

 contractions, and then beat normally again. 



