110 George Heuer. 



the fusion of these branches. One can readily demonstrate out- 

 growing branches in injected material, and from the appearance of 

 the peripheral ends of these branches and by the section one feels 

 reasonably sure that the injection has been complete. Moreover, if 

 one takes a series of embryos from 8.5 to 11 cm, long, injected from 

 the same place along the thoracic duct and under about the same 

 pressure, he finds in each succeeding larger embryo a more complete 

 plexus formation. 



Fig. 10. — Loop of small intestine of an embryo 10 cm. long to show the 

 development of the submucosal plexus from the primary loops shown in Fig. 9. 



The plexus thus formed in the submucosa never becomes complex 

 and close-meshed. In younger embryos it appears most complex, 

 for here the primary lymph ducts are close together. With the in- 

 crease in the size of the embryo and the elongation of the intestine, 

 it becomes a wider meshed and less complex appearing structure 

 and is recognized as the plexus of large vessels in embryos 16 cm. 

 long, as in Fig. 14, and in new-bom and adult pigs. 



From the primary submucosal plexus above described, there is 

 developed a second lymphatic plexus in the mucous membrane of 

 the intestine, namely, a plexus in the mucosa at the base of the villi. 

 From a study of the material at hand,it is believed that this plexus, 



