34 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



its first appearance in the form of a series of independent and 

 discontinuous vesicles, which can neither be injected from the 

 veins at points contiguous to them, from the subocular lymph 

 sacs, nor from the more caudally situated anlagen of the lateral 

 pharyngeal lymphatic which can be injected from the veins. 

 These anterior independent anlagen subsequently become con- 

 nected with one another and with the more caudally situated 

 anlagen of the lateral pharyngeal lymphatic, to form a con- 

 tinuous vessel which can then be injected from the veins along 

 its entire extent, and which finally establishes a communication 

 with the subocular lymph sac. After this confluence is com- 

 pleted we meet with a condition similar to that shown in figure 10. 



The progressive appearance of the independent anlagen of this 

 anterior portion of the lateral pharyngeal lymphatic is well illus- 

 trated by a series of reconstructions which were made of in- 

 jected embryos of the steelhead and rainbow trout. 



In a sixteen-day steelhead trout (fig. 5) a single independent 

 anlage (3') has alone made its appearance on the right side of the 

 embryo (left side of figure) which lies about opposite the first 

 efferent aortic arch (16). In a seventeen-day steelhead trout 

 (fig. 6) similar corresponding, and other independent anlagen 

 (3') have made their appearance on both sides of the embryo, 

 and the position occupied by them now clearly indicates the course 

 subsequently followed by the anterior portion of the lateral pha- 

 ryngeal lymphatic. From this point on, if we follow thefurther 

 development of these anterior independent anlagen (3') in the 

 rainbow trout, we find on the twentieth (fig. 8) and twenty-first 

 days (fig. 9) that they have also made their appearance on both 

 sides of the embryos, and that on the twenty-first day (fig. 9) 

 they have reached a stage of development which immediately 

 precedes that in which they have become confluent to form a 

 continuous vessel (3, fig. 10). 



The above-mentioned reconstructions were especially chosen 

 from among others in order to illustrate the principle that the 

 anterior portion of the lateral pharyngeal lymphatic is formed 

 through the concrescence of independent and discontinuous 

 lymph vesicles. They by no means illustrate completely, how- 



