40 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



Coincident with or soon after the appearance of the cardino- 

 Cuvierian lymph sacs, other lymph sacs make their appearance 

 contiguous to the precardinal vein in the neighborhood of the 

 caudal end of the otocyst. The otic lymph sacs (3"), as these 

 may be termed, are shown in figures 3 and 4 which are recon- 

 structions of the left and right sides, respectively, of a fifteen- 

 day steelhead trout embryo. These lymph sacs, like those in 

 the cardino-Cuvierian district, may also establish a communica- 

 tion with the precardinal vein. On the right side of the fifteen- 

 day steelhead trout embryo (fig. 4) the cranial end of the otic 

 lymph sac (3") lies fairly close to the precardinal vein (6) and, 

 although the vein was fully injected, as shown in a section taken 

 through the sac (3", fig. 36) the sac is not connected with the 

 vein (6), nor has the injecta entered the sac. On the left side of 

 the same embryo the otic sac (3", fig. 3) is also independent of 

 the vein (6) but in this case an extension from the vein runs out 

 in the direction of the sac. 



As in the case of the lymph sacs in the cardino-Cuvierian 

 district, an examination of the reconstructions of the later stages 

 shows that variations also occur as regards the relations of the 

 otic lymph sacs to the veins. In the sixteen-day steelhead trout 

 embryo (fig. 5) the otic lymph sacs (3") communicate freely 

 with the precardinal veins on both sides of the embryo, and the 

 relations which the sac of the right side bears to the vein re- 

 sembles a condition previously described by Huntington and 

 McClure ('10, page 203) as 'fenestration.' In the seventeen- 

 day steelhead trout (fig. 6) and in the nineteen (fig. 7) and 

 twenty-day (fig. 8) rainbow trout no communication exists be- 

 tween the anlagen of the lateral pharyngeal lymphatic and the 

 veins in the neighborhood of the caudal end of the otocyst. In 

 the twenty-one-day rainbow trout (fig. 9) an otic communica- 

 tion (13) is present on the left side of the embryo, and in the 

 twenty-two-day rainbow trout (fig. 10), in which the cardino- 

 Cuvierian and otic lymph sacs have become confluent to form a 

 continuous channel, the otic communication (13) is present only 

 on the right side. 



