PRECARDINAL (JUGULAR) LYMPHATIC 45 



right side of the embryo which may possibly communicate with 

 the otic lymph sac (3") through an exceedingly narrow inter- 

 cellular connection. This anlage (5"), as shown in section (fig. 

 36), lies closely in contact with the precardinal vein (6) and, as 

 the otic lymph sac (3") does not 'communicate with the vein, 

 neither, the otic lymph sac nor this anlage of the precardinal 

 lymphatic has received any injecta from the vein. In a sixteen- 

 day steelhead trout (fig. 5) two of these earliest anlagen(5 // ) 

 have made their appearance and they not only communicate in 

 this embryo with the otic lymph sacs (3"), but also through the 

 latter with the veins at the otic communication (13). From the 

 conditions shown in the fifteen and sixteen-day steelhead trout 

 embryos, one might infer that these earliest anlagen of the pre- 

 cardinal lymphatics were not formed independently of the otic 

 lymph sacs but were extensions of the latter, and such may pos- 

 sibly be the case for these particular anlagen. In view of the 

 circumstance, however, that in relatively much later stages of 

 development (figs. 6, 7 and 8) these same anlagen (5") may 

 also be found to be independent of the otic lymph sacs (3"), I 

 am lead to believe that they arise independently of the latter 

 and secondarily connect with them. In other words, the inde- 

 pendent character of these anlagen (5") in figures 6, 7 and 8, 

 probably indicates a condition in which the establishment of a 

 connection between them and the otic lymph sacs (3") has been 

 temporarily delayed (see Section XI, p. 50). 



We now pass to a consideration of those independent anlagen 

 of the precardinal lymphatics which arise remote from the otic 

 lymph sacs and remote from the typical points at which the lym- 

 phatics of the trout communicate with the veins. 



In general, these anlagen of the precardinal lymphatics may be 

 divided into two groups: One of which is situated posterior -and 

 the other anterior to the anlagen which arise contiguous to the 

 otic lymph sacs. The position occupied by the more posterior 

 anlagen is shown on the left side of figure 7 which is a recon- 

 struction of a nineteen-day rainbow trout embryo. This anlage 

 (5"') lies at about the level of the third efferent aortic arch (18) 

 and, as far as can be determined, does not communicate with the 



