LYMPH-FLOW AND LYMPHATICS, CHICK EMBRYOS 411 



Support is lent to this view by the fact that the main caudal 

 vein, into which the intersegmental coccygeal veins empty, 

 soon enters the mesonephros and breaks up into capillaries and 

 the resistance to be overcome would thus be greater than in the 

 neck veins which enter the duct of Cuvier near the point where 

 the lymphatics connect with them. Further evidence for this 

 hypothesis will be considered later in connection with various 

 observations on the early circulation in the posterior lymphatics. 



In chicks of approximately 6 to 6| days (average length 18 mm.) 

 the posterior lymph heart begins to pulsate. The early con- 

 tractions of the lymph heart have been described in another 

 publication. 10 In this paper Dr. Clark and I stated that the 

 early pulsation of the lymph heart is closely associated with the 

 periodic movements of the embryo, several beats occurring with 

 every spasm of movements, and that during the first day and a 

 half of pulsation, this connection is inseparable, the lymph heart 

 beats ceasing altogether when the body movements are paralyzed 

 with chloretone. The first pulsations commence at a time when 

 the lymph heart is still in the form of a plexus. 



In an embryo of the stage in which the lymph heart is just 

 beginning to contract, scattered knobs of blood are still present 

 in the lymphatics of the pelvis. The lymph heart shows as a 

 translucent area at the angle between the tail and the pelvis. 

 Contractions of this region occur at the time of the body move- 

 ments and are plainly visible although they are feeble in com- 

 parison with the pulsations seen in older chicks. In the interval 

 of rest between spasms (about 40 seconds in duration) the lymph 

 heart fills up with blood and the various vessels, of which it is 

 composed, then become visible. When India ink granules were 

 injected into the lymphatics of the pelvis, at this stage, they 

 moved posteriorly, taking a slow and winding course, into the 

 lymph heart plexus, and from there into the intersegmental 

 veins of the tail. If a lymph heart pulsation occurred while the 

 granules were moving down over the pelvis, they were forced 



1" E. L. Clark and E. R. Clark, On the early pulsations of the posterior lymph 

 hearts in chick embryos; their relation to the body movements. Jour. Exp. 

 Zool., vol. 17, no. 3, 1914. 



