124 CARNEGIE INSTITUTION OF WASHINGTON. 



nels are formed in the prevertebral venous plexus, which thus becomes 

 a part of the inferior vena cava. The inferior vena cava may therefore 

 be said to have a ventral segment and a dorsal or post-renal segment, 

 the ventral segment coming from the omphalo-mesenteric and mesial 

 cardinal veins and the dorsal segment from the prevertebral plexus. 



The azygos and hemiazygos veins are new longitudinal veins which 

 develop as an adjustment of the drainage which is due to the disap- 

 pearance of the Wolffian body and the changes in the adjacent body- 

 wall. They are, however, entireh' distinct from the posterior cardinal 

 veins, which disappear with the Wolffian body. The azygos veins 

 develop entirely in the prevertebral plexus. They, however, anasto- 

 mose freely with the cardinal system and in a way replace it. For, as 

 the posterior cardinal veins diminish in size the azygos veins grow 

 larger, assuming a drainage of the spinal veins with their tributaries. 

 Thus at a certain period the two are of about the same size and can then 

 be seen draining into the duct of Cuvier as separate veins, the azygos 

 maintaining a more dorsal position than the posterior cardinal. Sub- 

 sequently, as the posterior cardinal continues to dwindle, its point of 

 termination migrates from the duct of Cuvier downward along the 

 now relatively large azygos vein, into which it drains until it finally 

 disappears. 



In Dr. Sabin's paper there is included an historical survey of injec- 

 tion methods, with a critical description of the more recent technique. 

 Further work concerning the early development of the blood-vessels of 

 the chick has been under way during the past year, a preliminary report 

 of which was read at the St. Louis meeting of the American Association 

 of Anatomists. 



In our last report it was stated that the early lymphatics in the chick 

 which are destined to form the posterior lymph heart arise from the 

 adjacent veins and immediately fill with blood which backs into them. 

 Within a few days the embryonic lymph heart thus formed begins to 

 pulsate. These first movements are described in a study by E. L. 

 Clark and E. R. Clark. 



These authors find that the pulsation of the lymph heart first appears 

 in embryos of six or seven days (19 to 22 mm.) and that, at this earliest 

 stage, the beating of the lymph heart is intimately connected with the 

 periodic muscular movements of the embryo. Lymph-heart contract 

 tions accompany the periodic spasms, but never occur in the interim 

 between the body movements. Each beat is invariably accompanied 

 by a contraction of the tail. When the body movements are paralyzed 

 by chloretone the lymph-heart pulsations also cease. In successive 

 later stages they find a gradual increase in the independence of the 

 beating lymph heart. First, the pulsations become dissociated from 

 the tail contraction, although still occurring only during the periods of 

 body movements. Then there is a series of stages in which the lymph 



