THORACIC DUCT IN THE CHICK 135 



Stromsten (16) in his account of the development of the tho- 

 racic duct in turtles arrived at a like conclusion, stating that 

 "the development of the peri-aortic lymphatic plexus in the 

 loggerhead turtle is immediately preceded by the formation 

 of isolated, independent spaces. They (the spaces) cannot be 

 injected . . . ." (p. 354). "The intercellular spaces thus 

 formed enlarge and fuse together to form lymphatic lacunae. At 

 a later stage the lacunae acquire an endothelial lining and become 

 the isolated anlagen of the thoracic duct" (p. 356). 



As regards the thoracic duct in the chick, it^will be my object 

 in this article (1) to demonstrate its origin by confluence of inter- 

 cellular spaces in the mesenchyme, independent of the veins, and 

 to reconsider the significance of the mesenchymal cords described 

 by Sala in their relation to the developing lymphatics; (2) to dis- 

 cuss the establishment of the morphological drainage line of the 

 thoracic duct and the means by which this duct and the jugular 

 lymph sacs communicate; and (3) to show that the organization 

 of the avian thoracic duct corresponds in type with that estab- 

 lished in reptiles and mammals. 



II. MATERIAL 



Embryos of the domestic fowl (Gallus gallus) have been used 

 chiefly on account of the certainty in procuring the critical 

 stages. Some embryos of the English sparrow (Passer domesticus) 

 have also been used. Of this material I have examined thirty-two 

 individual embryos in serial sections, comprising twenty-seven 

 chicks and five sparrows. Four of the chicks were injected with 

 India ink through the umbilical vein (table 1). 



Unfortunately the sparrow embryos, of which series nos. 123, 

 124, 126, 154 and 509 were examined, were not measured and 

 could be judged as to stages of development only by comparison 

 with the chicks. 



The embryos were fixed in vom Rath's, Bouin's, or Zenker's 

 fluid (some in Zenker-formol), Bouin's fluid giving the best 

 results with the least shrinkage. The sections were cut in paraffin 

 and stained on the slide by one or the other of the following 

 methods. After fixation in vom Rath's mixture, the staining was 



