16 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



munications which formerly existed in the embryo, since cer- 

 tain of these communications may never have been formed at the 

 typical points. Such a condition is shown in the twenty-two day 

 rainbow trout embryo (fig. 10) in which the otic communication 

 (13) is present only on the right side. In general, such variations 

 as those mentioned above would fall in line with those observed 

 in mammals (Huntington and McClure '08; and McClure and 

 Silvester '09). Here we know that the points of communication 

 which the jugular lymph sacs establish with the veins fall within 

 two typical districts of communication (jugulo-subclavian and 

 common jugular angles), and that communications may be 

 established within only one of the two or within both of these 

 districts. 



The communication established between the subocular lymph 

 sac and the lateral pharyngeal lymphatic on the twenty-second 

 day (fig. 10) is, as far as I can determine, not permanently re- 

 tained in quite advanced embryonic stages and in the adult. 

 At a certain period after hatching the subocular lymph sac be- 

 comes detached from the lateral pharyngeal lymphatic so that 

 the sac ceases to drain through the latter into the veins. Also, 

 after its detachment, the subocular lymph sac of the trout ap- 

 pears to remain detached from the lateral pharyngeal lymphatic 

 during all subsequent stages of development, and neither estab- 

 lishes any further communication with the veins, nor with any 

 other portion of the lymphatic system. In correlation with the 

 loss of the subocular lymph sac as an organic part of a con- 

 nected lymphatic system, a new lymphatic channel makes its 

 appearance in the embryo, the superficial facial lymphatic, which 

 aids in draining the region of the head formerly drained by the 

 subocular lymph sac. The superficial facial lymphatic (21), as 

 shown in the 17.5 mm. brook trout (fig. 11), forms the direct 

 anterior continuation in the head region of the lateral pharyngeal 

 lymphatic (3). 



It is difficult to establish definitely for the three species of trout 

 embryos studied, the exact time at which the detachment and 

 separation of the subocular lymph sac from the lateral pharyngeal 

 lymphatic occurs. The sacs were invariably found to be de- 



