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 hving 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 completelj^ 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 

 l3miphatic 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 freelj^ 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 ser\'ice 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. 



