DEPARTMENT OF EMBRYOLOGY. 125 



heart contracts more and more frequently during the period of rest^ 

 although still beating a number of times during each spasm. When 

 chlorotone is added a larger number of single pulsations occur inde- 

 pendently at irregular intervals. At these stages the lymph heart is 

 capable of entirely independent function, but is influenced in its rhythm 

 by the periodic spasms of body movements. 



Finally a stage is reached in which the lymph-heart pulsations are 

 uninfluenced in any way by the body movements. During all of these 

 stages mechanical stimuli, such as pressure over the surface with a fine 

 needle or direct puncture of the myotomes, fail 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 causes tail contractions together with the pulsations, while at 

 later stages it stimulates the lymph heart alone. 



This work has now been extended by E. L. Clark to include a study 

 of the first lymph flow in the superficial lymphatics in chicks from five 

 to nine days old. After the lymphatic plexus in the tail of the chick 

 forms the posterior lymph heart it gradually extends anteriorly over 

 the body to meet a like extension which arises in the neck. These two 

 networks unite over the hip. At this time the lymphatics remain filled 

 with blood which leaks in from the veins. As the flow of lymph begins 

 they empty themselves of blood, first through the neck lymphatics and 

 then through those which flow into the posterior lymph heart. Many 

 experiments were made to test this flow by injecting india ink into the 

 lymphatics of the hving chick and observing it under favorable condi- 

 tions. Only a preliminary account of this study has been published. 



Professor E. R. Clark has also published an account of the general 

 anatomy of the lymphatic system, as well as of a unique variation of the 

 thoracic duct in man, which appears as No. 3 of the Contributions to 

 Embryology. In this specimen the region normally occupied by the 

 thoracic duct was obstructed and therefore the lymph flow from the 

 lower part of the body followed the primitive lymphatics under the 

 skin to the axilla and established there a "thoracic duct" outside of 

 the thorax, which remained throughout life. A knowledge of the early 

 lymphatics and the circulation through them makes the anomaly 

 inteUigible. 



A preliminary account of Dr. R. S. Cunningham's study on the 

 development of the lymphatics in the lung of the pig has been pub- 

 Ushed and a final report is being prepared for press. 



