26 DEVELOPMENT OF LYMPHATIC SYSTEM, FISHES 



and, in one embryo the sac was included in six sections on each 

 side of the body (fig. 22) . All of the above-mentioned sections 

 were ten micra in thickness. 



It is thus seen, within a particular group of trout embryos, of 

 exactly the same age and developed under similar conditions of 

 temperature, that every gradation in the bilateral estabhshment 

 of the subocular lymph sacs can be observed; from their very 

 first appearance in the embryo until they have approached in 

 size and importance a degree of development which may even be 

 found in embryos on the fifteenth day after fertilization (fig. 23) . 

 Compare figures 22 and 23, which are photomicrographs of sec- 

 tions taken through the subocular lymph sacs of steelhead trout 

 embryos, developed under similar conditions, on the fourteenth 

 and fifteenth days, respectively, after fertilization. It is un- 

 necessary to state that a similar set of observations could be 

 made upon other groups of the same, or upon other groups of 

 different species of trout embryos, which have developed under 

 the same or under different conditions of temperature. I think 

 there can be no question, therefore, that the clear areas (1) 

 shown in figure 19 constitute the earliest anlagen of the subocu- 

 lar lymph sacs and to these we will now turn our attention. 



The origin of these earliest anlagen of the subocular lymph 

 sacs is naturally the main question at issue. Do these anlagen 

 communicate with the veins at the time of their inception and 

 can they be injected from the veins? Do these early anlagen 

 at first possess what one might regard as an endothelium? Are 

 these early anlagen of the subocular lymph sacs connected with 

 the endothelium of the veins by solid cords of cells which might 

 indicate that they are outgrowths from the veins? 



Do the anlagen of the subocular lymph sacs communicate 

 with the veins at the time of their inception and can they be 

 injected from the veins? 



As the result of numerous observations made on all three species 

 of trout embryos and without exceptions, it has been my experi- 

 ence that the study of sections completely corroborates all of the 

 above-mentioned observations made on the living trout embryo. 

 Barring self-evident extravasations, I have been unable to inject 



