42 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



in the otic and cardino-Cuvierian lymph sacs at a corresponding 

 stage. I therefore believe that the balance of evidence favors 

 the view that, like the subocular lymph sac and the independent 

 anlagen of the more anterior portion of the lateral pharyngeal 

 lymphatic, the lymph sacs in the otic and cardino-Cuvierian dis- 

 tricts develop in situ in the mesenchyme and that, while certain 

 of these sacs may secondarily establish venous connections, 

 others may enter directly into the formation of the lateral 

 pharyngeal lymphatic without previously joining the veins. 



Felix ('97) has described the development of the aorta and 

 cardinal veins in the trout and salmon and finds that these ves- 

 sels not only arise in situ but that their lumina are formed by a 

 confluence of vascular spaces w^hich make their appearance in a 

 discontinuous manner in a solid cord of cells. The recent ex- 

 perimental work of Stockard ('15) on Fundulus has verified these 

 results in all essential details. If we compare the development 

 of the lateral pharyngeal lymphatic with that of the aorta and 

 cardinal veins, w^e find that the lateral pharyngeal lymphatic, 

 like the aorta and the cardinal veins, presents a temporary onto- 

 genetic condition in which a continuous channel is invariably 

 preceded by a series of discontinuous vascular spaces. This is an 

 incontrovertible fact which can be definitely established by the 

 aid of the injection method and by a study of sections. Such 

 a similarity certainly signifies a common genetic plan of develop- 

 ment for all of these independent vascular spaces, and for the 

 endothelium which forms their walls, rather than that the plan of 

 development for the lymphatics differs from that of the arteries 

 and veins. This question will be more fully considered in con- 

 nection with another topic (Section XIII, p. 57). 



VIII. THE DEVELOPMENT OF THE SUPERFICIAL FACIAL 

 LYIVIPHATIC IN THE TROUT 



It has already been stated 'that the subocular lymph sac of the 

 trout embryo subsequently severs its connection with the lat- 

 eral pharyngeal lymphatic (page 23) and that the latter is then 

 continued into the head region as a vessel which has been desig- 

 nated as the superficial facial lymphatic. This vessel (21) is 



