392 E. L. CLARK AND E. R. CLARK 



In the matter of a common nerve supply for the myotomes 

 and the lymph heart, our study of sections yielded only negative 

 results, since we were unable to find any nerves in the wall of 

 the lymph heart at any of the stages studied. However, further 

 study with special nerve stains is necessary before this possi- 

 bility can be excluded altogether. 



We have already mentioned the fact that, duriMg the earliest 

 stage of its pulsation, the lymph heart lies in close proximity to 

 the transitory lateral portion of the myotome. It is quite possi- 

 ble, therefore, that the contraction of the myotome, at this 

 earliest stage, might stimulate the muscle of the lymph heart 

 to contract, merely mechanically, without the presence of an 

 actual connection between the two. In chicks of eight to nine 

 days, with the disappearance of this part of the myotome, the 

 lymph heart comes to occupy an isolated position in the mesen- 

 chyme. At this stage, however, the pulsation of the lymph 

 heart is still influenced in its rhythm by the periodic contractions 

 of the embryo. In an embryo of eleven days, the lymph heart 

 has shifted its position and it now lies in close proximity to the 

 dorsal muscle. But in this stage, in spite of its situation, the 

 lymph heart is entirely independent in its beating, from the 

 contraction of the rest of the musculature. Therefore, although 

 the phenomena of the earliest stage of the lymph heart pulsa- 

 tion might be accounted for by the proximity of the myotome, 

 which by its contraction stimulates the muscle of the lymph 

 heart directly, the gradual manner in which the lymph heart 

 pulsation becomes dissociated from the body contractions can- 

 not be explained in this way. For, unlike the change in their 

 physiological relationship, the change in the relative position 

 of the myotome and the lymph heart muscle is sudden and not 

 gradual. 



In injecting the superficial lymphatics in living chicks, we have 

 often observed that the Ijonph heart contracted as the fluid 

 entered it. It is therefore capable of reaction to a stimulus from 

 within as well as to the mechanical stimulation of its wall, and 

 the gradually increasing independence of the lymph heart pul- 

 sations from the contractions of the body musculature may be 



