390 E. L. CLARK AND E. R. CLARK 



the body movements are paralyzed by chloretone, the Ijrmph 

 heart pulsations also cease. 



In successive later stages, we find a gradual increase in the 

 independence of the beating lymph heart. First, the pulsations 

 become dissociated from the tail contraction, although still occur- 

 ring only during the periods of body movements. Then we find 

 a series of stages in which the lymph heart contracts more and 

 more frequently dm-ing the period of rest, although still beating 

 a number of times during each spasm. When chloretone is 

 added, at these stages, a larger number of single pulsations occur 

 independently, at irregular intervals. At these stages, the lymph 

 heart is capable of entirely independent function, but is influ- 

 enced, in its rhythm by the periodic spasms of body movements. 



Finally, a stage is reached in which the lymph heart pulsa- 

 tions are uninfluenced, in any way, by the body movements. 

 During all of these stages, mechancial stimuli, such as pressure 

 over the surface with a fine needle, or direct puncture of the 

 myotomes, failed to influence the body movements. Although 

 the lymph heart does not respond to pressure over the surface, 

 it always contracts when its wall is actually pierced. At the 

 stage in which the lymph heart is not yet independent, such a 

 puncture instigates tail contractions along with the lymph heart 

 pulsations, while at later stages it stimulates the lymph heart 

 alone. 



DISCUSSION 



In connection with our observations of the early pulsations of 

 the lymph heart, we made serial sections of all the stages studied. 

 In every case, the embryo sectioned was one which had been 

 observed in the living and in which the movements and lymph 

 heart pulsations had been recorded. From the study of these 

 cross sections, however, we were unable to discover a definite 

 anatomical relationship corresponding to the close functional 

 association which exists, at first, between the lymph heart and 

 the body musculature. 



The following possibilities have suggested themselves in the 

 course of our observations. It is possible: 



