Florence E. Sabin 



369 



In the first diagram, Fig. 10, tlie step in advance beyond the stage of 

 Fig. 9 is in the proliferation of the lymphatic capillaries. The sac has 

 been completely cut up into ducts. The entire node consists of a plexus 

 of lymphatics which differs in no way from the plexus in the skin 

 pictured in my first paper. There are the same swollen bulbs, the same 

 blind sprouts and slender channels. The connective tissue bridges are 

 similar to those of the preceding stages. They contain many dividing 

 cells but no true wandering cells. In the bridges is an abundant plexus 

 of blood capillaries which are not shown in the 

 diagram. This diagram might also represent any 

 lymph node which develops in a plexus. 



To sum up, the figure marks the culmination of 

 the first stage of the development of the lymphatic 

 nodes in early embryos, namely, the stage in which 

 the node consists of a plexus of lymphatic capil- 

 laries separated by bauds of connective tissue 

 which is denser than the surrounding tissue. This 

 stage is shown in Kling's ' models. Fig. 1. The 

 connective tissue is embryonic in type, consisting 

 of a net work of granular protoplasm with a few 

 fibrils and with many nuclei. The bands or 

 bridges have blood capillaries and the increase in 

 connective tissue does not take place independently 

 of them. There are no true wandering cells out- 

 side of the blood capillaries. It is the stage of 

 lymphatic ducts and pure connective tissue bridges. 

 All of the nodes of the early embryos, the primary 

 nodes in the sense of Gulland pass through this 

 stage. That is to say, the nodes which develop in 

 the long plexus in the neck from which ducts 

 radiate to the face, neck, fore legs and thorax 

 (Fig. 6) ; or the node which comes in the in- 

 guinal region at the point where tlie ducts radiate over the abdominal 

 wall and hind legs; or in the node over the crest of the ileum where they 

 radiate over the back (see Fig. 5, Vol. Ill, p. 188). All of these nodes 

 come in places, where plexuses are formed because ducts radiate over a 

 wide area, which is shown well in the figure just quoted. They are 

 primary nodes in the sense of Gulland because they develop early and 

 drain large capillary areas. It will be shown subsequently that lymphatic 



Fio. 10. Diagram of 

 the primary lymph node 

 in an embryo pig- 7 cm. 

 lonjr. X about 53. The 

 lymphatics are in solid 

 black and the connective 

 tissue bridges are dotted. 



Ibid 



