18 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



a 12.5 mm. embryo of Amia between the subocular sac and the 

 lateral pharyngeal lymphatic, the subocular lymph sac, as in the 

 trout, appears to remain detached from the veins and from the 

 remainder of the lymphatic system during all subsequent stages 

 of development. It is therefore seen, in both ganoids and the 

 trout, that the subocular lymph sacs function only temporarily 

 in the embryo as lymphatics which drain into the veins, and that 

 the route by way of which they drain into the veins in ganoids 

 differs from that in the trout. 



Another feature of interest is that the detachment of the sub- 

 ocular lymph sac from the veins occurs in ganoids at a relatively 

 much earlier stage of development, than its detachment from the 

 lateral pharyngeal lymphatic occurs in the trout. In correla- 

 tion with this early detachment of the sac in ganoids, as com- 

 pared with that in the trout, the superficial facial lymphatic 

 makes its appearance in ganoids at a relatively'' much earlier stage 

 of development than is the case in the trout (compare 21 in figs. 

 11, 12 and 13 with fig. 10). 



A comparison of the lymphatic vessels found in an advanced 

 embryonic stage of Amia (fig. 13) with those found in a 17.5 mm. 

 brook trout (fig. 11), shows that the fundamental plan of the 

 Ijnnphatic sj^stem in the head and pharynx is the same in each. 

 The precardinal lymphatics (5 in fig. 13) anastomose less fre- 

 quently with the lateral pharyngeal IjTiiphatic (3) in Amia than 

 is the case in the trout. In both cases the precardinal lymphatics 

 receive the same class of tributaries, however, and drain into the 

 veins at corresponding t^^pical points (9, cardino-Cuvierian 

 and 2, medial pharyngeal communications, figs. 11 and 13). 



W. F. Allen ('06) has described as the 'superficial facial' 

 lymphatic in the adult Scorpaenichthys, a vessel which un- 

 doubtedly corresponds to the superficial facial lymphatic men- 

 tioned above as being present in the embryos of Amia, Lepidos- 

 teus and the trout (compare 21 in figs. 11 and 13 of the trout and 

 Amia with S. Fac. in Allen's figs. 4 and 5 of Scorpaenichthys). 

 The 'profundus facial' lymphatic described by Allen in Scor- 

 paenichthys may possibly correspond to the subocular lymph 

 sac of the trout and ganoids and it is of interest to note that 



