10 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



and discontinuous anlagen of the precardinal lymphatics (5') 

 since these do not as yet communicate with the continuous 

 lymphatic system as a whole. The above-mentioned continuous 

 lymphatic system, as well as the veins, can also be readily in- 

 jected from the subocular lymph sacs. 



Observations made upon the living trout embryo at this stage 

 of development have also shown that, in the absence of lym- 

 phatico-venous valves, blood may pass from the veins into the 

 lymphatics. In a great number of instances blood was observed 

 to pass from the precardinal vein into the lateral pharyngeal 

 lymphatic of a living trout embryo and, after filling completely 

 the subocular lymph sac, to flow back into the veins. Figure 15 

 is a section of a twenty-day steelhead trout embryo which passes 

 through both subocular lymph sacs and in which it is seen that 

 the sac on the right side is completely filled with blood, while 

 that on the left side is empty. In all such cases as those men- 

 tioned above, the blood-filled subocular lymph sac has invari- 

 ably established its connection with the lateral pharyngeal 

 lymphatic and, in the case of the twenty-day steelhead trout 

 embryo (fig. 15), this connection was established only upon the 

 right side. In trout embryos older than twenty-two days, 

 and in which lymphatico- venous valves have been formed, the 

 application of chloretone was found to vitiate the normal func- 

 tion of the valves. Blood would even then flow freely into the 

 lymphatics from the veins and fill up completely all of the 

 lymphatic channels, including the subocular lymph sacs, which 

 had established a communication with the veins. When such 

 embryos were removed to water in which no chloretone was pres- 

 ent, the blood usually flowed back into the veins from the 

 lymphatics. These so-called blood-injected embryos proved of 

 great service in many instances, in following the course of lym- 

 phatic channels. In abnormal living trout embryos, especially 

 those with spinal curvature, and at an age at which lymphatico- 

 venous valves should be present, blood was frequently found 

 in the subocular lymph sac and in the lateral pharyngeal lym- 

 phatic. 



