THE LATERAL PHARYNGEAL LYMPHATIC 39 



significance, as it is by means of these sacs that permanent com- 

 munications are subsequently estabHshed between the lymphatics 

 and the veins in the cardino-Cuvierian district. The presence, 

 therefore, of a connection between these sacs and the veins, 

 as met with in certain stages, does not necessarily indicate that 

 the cardino-Cuvierian lymph sacs have been derived from the 

 veins, since their connection with the veins may have been formed 

 secondarily; either through a growth or extension of the endo- 

 thelium of the veins, or by a further in situ differentiation into 

 endothelium of the mesenchyme that intervenes between them. 

 What the subsequent fate of these individual lymph sacs 

 might be, can best be surmised by observing the conditions found 

 in a consecutive series of embryos. An examination of such a 

 series shows considerable variation as regards the number and 

 location of the communications which may be established be- 

 tween the anlagen of the lateral pharyngeal lymphatic and the 

 veins in the cardino-Cuvierian district. These lymph sacs (3'") 

 may establish a communication with the veins some distance 

 anterior to the cardino-Cuvierian junction (9, figs. 3 and 4) ; they 

 may communicate with the veins at two points, one anterior and 

 the other posterior to the cardino-Cuvierian junction (9, fig. 5, 

 right side of embryo) ; they may communicate with the veins 

 at the cardino-Cuvierian junction (9, fig. 6, both sides of em- 

 bryo) ; they may communicate with the veins at two points at 

 the cardino-Cuvierian junction (9, fig. 7, left side of embryo and 

 9, fig. 10, both sides) ; or, they may communicate with the veins 

 at three points, one at the cardino-Cuvierian junction and at 

 two points anterior to the latter (9, fig. 9, left side of embryo). 

 An examination of the reconstructions of the later stages also 

 shows that lymph sacs are met with in the cardino-Cuvierian 

 district which do not communicate with the veins. Two of these 

 independent sacs (3'") are shown in the reconstruction of a fifteen- 

 day steelhead (fig. 3), and one on the right side of the twenty-day 

 rainbow trout (fig. 8). In neither case have these independent 

 sacs received the injecta, nor can any connection be observed 

 between them and the veins. 



