THE MEDIAL PHARYNGEAL LYMPHATIC 49 



velopment are more easily followed in ganoids than in the trout. 

 The earliest anlage of the medial pharyngeal lymphatic was met 

 with in a 7.5 mm. embryo of Amia (6.81 mm., measured by sec- 

 tions) and is shown in section in figure 40. This anlage (4') 

 was included in two sections (10 micra each) and, as shown in the 

 figure, it neither communicates with the precardinal vein (6) , nor 

 is it connected with the latter in this, or in any other section, by 

 a solid endothelial strand. A study of the later stages shows 

 that this independent anlage invariably establishes a connection 

 with the precardinal vein (4, figs. 12 and 13), and it can then be 

 easily injected from the veins before lymphatico-venous valves 

 are formed. The vascular system of the embryo from which 

 figure 40 is taken was fully reconstructed in order to prove that 

 the anlage in question was that of the medial pharyngeal lym- 

 phatic. Since this independent anlage was found to occupy 

 identically the same relative position in this embryo as that of 

 the medial pharyngeal sac of later stages, no possible doubt can 

 exist regarding it. 



The anlagen of the lymphatic system, which develop in close 

 relation to the typical points at which the lymphatics establish 

 communications with the veins, have been described by Hunt- 

 ington and McClure ('10) in mammals as 'venolymphatics.' 

 The term 'venolymphatic' may therefore be similarly applied to 

 those anlagen of the lymphatic system of fishes which develop 

 contiguous to the typical points at which the lymphatics com- 

 municate with the veins. These anlagen include the otic, the 

 cardino-Cuvierian and the medial pharyngeal lymph sacs in the 

 trout; the cardino-Cuvierian, the subocular and medial pharyn- 

 geal lymph sacs in ganoids. In view of the interpretation placed 

 by the writer upon the genesis of the lymphatics in general, the 

 use of the term 'venolymphatic,' we shall see (Section XIII, p. 

 57) , becomes entirely unnecessary in distinguishing these an- 

 lagen of the lymphatic system from those which develop elsewhere 

 in the body remote from the typical points of lymphatico-venous 

 entry. The medial pharyngeal lymphatic of Amia serves to illus- 

 trate the principle of lymphatic, as well as that of vascular develop- 

 ment, in general, for the reason that, being classed as a 'veno- 



