280 GEO. S. HUNTINGTON 



be sought to the somewhat puzzling temporary separation of the 

 jugular lymphsacs from the veins. This separation marks the 

 termination of their primary haemophoric activity. After the 

 process is accomplished their detachment permits them, on the 

 one hand, to join the systemic lymphatics, while on the other it 

 enables the then active rearrangement of the permanent venous 

 system to take place, unimpeded by direct connections with the 

 lymphatic terminals. 



A comparison of this developmental history of the jugular lymph 

 sac of the higher vertebrates, representing in these types an 

 anterior or cranial lymphatico-venous heart, with the results 

 obtained in recent investigations of the development of the pos- 

 terior or caudal lymphatico-venous heart, yields exceedingly inter- 

 esting and corroborative evidence in favor of the genetic inter- 

 pretation above outlined. 



The development of the caudal lymphatico-venous heart has 

 recently been studied by Allen (29) in Polistotrema (Bdellostoma) 

 stouti, by Stromsten (25, 26) in the loggerhead turtle, Thalasso- 

 chelys caretta, and by Fedorowicz (30) in Anure larvae (Rana 

 esculenta, R. temporaria, Bufo vulgaris, B. viridis). West, 

 working in the morphological laboratories of Princeton and 

 Columbia Universities, has conducted a reinvestigation along 

 modern lines of the development of the caudal lymphatico-venous 

 heart in the chick. 



Allen (29) finds that the caudal lyinphatic hearts of Polisto- 

 trema (Bdellostoma) stouti develop by the formation of isolated 

 mesenchymal spaces in the region of the anterior ends of the 

 two branches of the caudal vein. These spaces develop by the 

 breaking down of certain mesenchymal cell processes in the 

 centre, and the thickening of others to form the boundaries of 

 the cavity. Subsequently the mesenchymal partition between 

 the spaces and the caudal vein breaks down, establishing a 

 secondary lymphatico-venous connection of the caudal lymph 

 heart with the caudal vein, while the more distal isolated mesen- 

 chymal spaces develop, increase in size, unite and join the 

 mesenchymal cavity already connected secondarily with the 

 caudal vein. 



