44 Florence B. Babin. 



each other. In following the series cerebralward from the level of fig. 9 

 it is clear that the blood-filled lymphatics not only arch across the 

 midline dorsal to- the aorta, but they follow the border of the Wolffian 

 bodies lateral to the aorta. Above the adrenal bodies the Wolffian 

 bodies approach very close to the aorta, and some of the lymphatic 

 buds curve around the ventral surface of the aorta. Thus in a speci- 

 men 33 mm. long there is a plexus of blood-filled lymphatics surround- 

 ing the aorta and extending into the lower thorax as far as the cerebral 

 pole of the Wolffian bodies. At the cerebral end of the Wolffian bodies 

 there are large veins which curve ventral to the aorta and connect 

 the veins of the capsule of the Wolffian bodies. Some of the lymphatics 

 are near these median veins. 



The finding of the renal lymphatics in the blood-packed stage makes 

 it quite certain that the thoracic duct arises in two places: First, 

 the jugular stem, which can be injected from the left jugular sac and 

 develops long after the jugular sacs are entirely empty of blood; and, 

 secondly, the renal plexus, which surrounds the aorta and forms a defi- 

 nite cisterna chyli. 



These two observations, namely, (1) the presence of blood in one 

 part and its absence in the other, and (2) the fact that injections 

 prove a connection of the jugular stem with the jugular sac, and of 

 the abdominal plexus with the mesonephritic veins, make it quite cer- 

 tain that the two portions of the thoracic duct are distinct from each 

 other in embryo pigs measuring 23 mm., and hence that the thoracic 

 duct begins in two places. Practically the entire question at issue 

 between those of us who think that the lymphatics grow by their own 

 endothelial wall and those who do not centers around the question 

 of how the thoracic duct develops, or, to put it more specifically, how 

 these two lymphatic anlagen become connected. The discussion centers 

 around my specimen 23a, which Kampmeier studied and which he 

 uses as his most conclusive evidence of the theory of the growth of 

 lymphatics by the addition of tissue spaces. On the other hand, it 

 is my theory that the thoracic duct grows from these two anlagen from 

 the veins by the same method by which other lymphatic capillaries 

 can be seen to grow in a living specimen, namely, by the sprouting of 

 their endothelial wall. It is true that I have not yet sufficiently 

 mastered the difficulties of injecting the renal lymphatics to demon- 

 strate the progression of the thoracic duct and indeed it may not 

 prove possible to get as conclusive proof of the origin of the deep lym- 



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