DEVELOPMENT OF SUBOCULAR LYMPH SACS 23 



lymphatic, and the sac might then be erroneously interpreted as 

 an outgrowth of the latter (compare 1 in figs. 9 and 10). It 

 is also evident if one attempted to follow the development of the 

 lymphatics by injecting into the subocular sacs, that none of the 

 other lymphatics already established in the embryo (lateral and 

 medial pharyngeal and precardinal lymphatics, fig. 9), would re- 

 ceive the injecta until a communication had been established be- 

 tween the sacs and the lateral pharyngeal lymphatic; in which 

 case one might also erroneously infer that all of the lymphatics 

 of the head and pharynx had sprouted from the subocular sacs. 



The above observations can be easily verified on living trout 

 embryos and serve among the best examples I know of in proof 

 of the inadequacy of the injection method as a means of determining 

 even the presence in the embryo of the actual anlagen of the lymphatic 

 system. The injection method is still consistently employed by 

 Professor Sabin and is the one upon which her conception of the 

 development of the lymphatics, as continuous hollow outgrowths 

 from the veins, was originally based (Sabin '02). 



4. The subocular lymph sacs of the trout embryo subsequently 

 become detached from the lateral pharyngeal lymphatic (fig. 11). 



As stated on a preceding page (p. 16), the subocular lymph 

 sacs of the trout subsequently sever their connection with the 

 lateral pharyngeal lymphatic and, from this time on, apparently 

 neither establish any further communication with the veins, nor 

 with any other portion of the lymphatic system. Although the 

 independent character of the sac in the more advanced stages 

 can be demonstrated by the injection method, the extravasa- 

 tions produced by forcing the injecta through the lymphatico- 

 venous valves has proved this method to be unsatisfactory. 

 The most conclusive proof of the independent character finally 

 assumed by the sacs was obtained by observing the course fol- 

 lowed by the blood in the lymphatics of the living embryo, after 

 the latter had been subjected to a treatment of chloretone. In 

 such embryos (see p. 10) the blood was observed to flow from the 

 veins into the lateral pharyngeal lymphatic and thence into its 

 anterior continuation in the head region, the superficial facial 

 lymphatic, without entering the subocular lymph sac. 



