384 E, L. CLAEK AND E. R. CLARK 



no longer present in the plexus of the posterior lymph heart 

 region. In the living chick, this area has a swollen, translucent 

 appearance and, upon injection, a plexus shows up, which is 

 more compact and which is composed of fewer and larger vessels 

 than the lymphatic plexus of younger embryos. At this stage, 

 distinct localized pulsations of this clear area are noticeable in 

 living chicks. Physiologically, then, a posterior lymph heart 

 is now present. 



Embryos of this stage were kept alive and under continuous 

 observation for from 2 to 5 hours and records made of every 

 lymph heart contraction and of each periodic spasm of body 

 movements. It was found that the lymph heart beats occurred 

 invariably at the time of the periodic spasms and never in the 

 intervals between these body movements. Moreover we found 

 that, at this stage, a beat of the lymph heart was always accom- 

 panied by a movement of the tail. Tail movements occurred, 

 unaccompanied by any lymph heart contraction, but beats of the 

 lymph heart unaccompanied by a tail movement were never 

 observed. 



After an em.bryo of this stage had been observed for an hour 

 and this relation of lymph heart beats to the periodic body move- 

 ments recorded, chloretone (1 : 4000 in Ringer's solution at the 

 temperature of the chick) was dropped on the embryo. A min- 

 ute later the body contractions ceased and the chick remained 

 motionless for a period of fifteen minutes. During this time no 

 pulsation of the lymph heart was observed. As the effect of the 

 anaesthesia w^ore off the spasmodic contractions returned and 

 soon regained their fomier periodicity. The lymph heart beats 

 returned at the same time and accompanied the body spasms 

 as before and each beat was always associated with a contrac- 

 tion of the tail. It is evident, then, that at this earliest stage in 

 which definite pulsations of the posterior lymph heart are vis- 

 ible, the beating is inseparably connected with the periodic move- 

 ments of the embryo (charts 1 and 2: Stage 1). 



We found, however, that unlike the rest of the musculature 

 of the chick, the lymph heart muscle responds to direct stimula- 

 tion and always contracts when it is punctured. In chicks of 



