EARLY PULSATIONS OF LYMPH HEARTS 391 



1. That the lymph heart musculature is derived from the myo- 

 tomes and that there is for a time a connection between the two. 



2. That the muscle of the lymph heart is temporarily supplied 

 by the same nerves which supply the myotomes. 



3. That the lymph heart is merely stimulated mechanically 

 by the contraction of the nearby muscles. 



4. That, at ^ first, the contractions of the lymph heart result 

 from the same stimulus which brings about the periodic body 

 movements, and that this stimulus is gradually subordinated to 

 the stimulus caused by the increasing amount of lymph, brought 

 to the lymph heart by the lymphatic vessels from the fast grow- 

 ing allantois and from the posterior half of the chick. 



As regards the derivation of the musculature of the lymph 

 heart from the myotomes, we have been unable to reach a defi- 

 nite conclusion from sections alone. In five-day chicks, the ven- 

 tral extension of the myotome lies medial to the lymph heart 

 plexus, separated by two or three layers of mesenchyme cells. 

 During the succeeding day, this lateral portion of the myotome, 

 which lies between the dorsal and ventral parts, becomes thinner, 

 and in chicks of seven days and a few hours, only a few small 

 bundles of somewhat isolated muscle cells remain. In sections 

 of embryos of six and one-half days, with the oil immersion lens, 

 we have seen muscle fibrillae in the wall of the lymph heart, 

 which, at this stage, still retains the form of a plexus of lym- 

 phatic vessels. The muscle of the lymph heart, therefore, is 

 present at an earlier stage than was supposed by Sala, who asserts 

 that only mesenchyme is visible around the sac in embryos 

 younger than eight and one-half days. In chicks of six and one- 

 half to seven days, which is the stage at which the lymph heart 

 beats always synchronously with the body movements, the wall 

 of the lymph heart lies in close proximity to the thin lateral 

 portion of the myotome already referred to. But, as regards 

 the presence of a definite connection between the muscle fibrillae 

 in the wall of the lymph heart and those composing this transi- 

 tory portion of the myotome, we were unable to reach a positive 

 conclusion. 



THE JOURNAL OF EXPERIMENTAL, ZOOLOGY, VOL. 17, NO. 3 



