32 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



ocular sac of the trout often present a multilocular appearance 

 and, in this respect, resemble the conditions found in its original 

 anlage (fig. 21). Figure 26 represents such a section taken 

 through the anterior end of the left subocular lymph sac of a 

 twenty-two-day rainbow trout embryo. The subocular sac is 

 seen to be divided into three compartments by two strands of 

 mesenchymal tissue and faint traces of strands were also ob- 

 served in the sac of the opposite side when examined under high 

 magnification. Compare figure 26 with figure 21, which is a 

 section taken through the subocular sac soon after its first appear- 

 ance in the embryo. As such compartments are not met else- 

 where in the subocular sac, their presence at the cranial end of 

 the sac in the twenty-two-day trout embryo is undoubtedly 

 indicative of a primary and transitional condition, in which this 

 portion of the sac is still incomplete and is still in the process of 

 formation. Such a condition cannot be accounted for on the 

 ground that a single-chambered anlage of the sac (1), as shown 

 in figure 23, has gradually expanded forward. It is therefore 

 evident that the forward extension of the subocular lymph sac 

 takes place, not only by a growth of its walls which keeps pace 

 with the growth of the embryo but also, like the earliest anlage 

 of the sac (fig. 21), by the addition and confluence of independent 

 anlagen. 



VII. THE DEVELOPMENT OF THE LATERAL PHARYNGEAL LYM- 

 PHATIC IN THE TROUT 



It is by means of the anlagen of the lateral pharyngeal lym- 

 phatic that a communication is first established in the regions of 

 the head and pharynx between the lymphatics and the veins. 

 The earliest anlagen of the lateral pharyngeal lymphatic to 

 make their appearance in the trout embryo may establish com- 

 munications with the precardinal (jugular) vein near the caudal 

 end of the otocyst, at the cardino-Cuvierian junction, and at 

 almost any point between the two. These points of communi- 

 cation may be retained in the later stages and, as far as deter- 

 mined, constitute the only points of communication which the 



