LYMPHATICS IN FROG LARVAE 51 



the surrounding tissues, bear witness to the direct derivation 

 of the sinuses from undistended primary ducts which invaria- 

 bly carry similar processes, rather than from fusion of inde- 

 pendent rudiments. 



As in other peripheral end ducts, the numerous processes 

 growing out from the sinus walls, which doubtless serve as 

 collecting ducts of lymph from the region (Hoyer), appear 

 quite erratically in injections, the fluid being generally ab- 

 sorbed by the large sinus cavity, projecting points of the 

 walls alone indicating the position of the uninjected ducts. 

 Such pointed protrusions of the walls are conspicuous in fig- 

 ures 18, 19, 24 and 30. The slender tubular collecting proc- 

 esses are demonstrated in different specimens, in a series, at 

 various points along 1 the lower border of the orbit, forming 

 a more or less complete chain. The orbit is thus drained into 

 the temporal sinus, and also posteriorly, into the lymph heart 

 plexus, through vessels which pass over the ear vesicle (figs. 

 19 and 30). When not filled too full, the tubes are seen to be 

 delicate thin-walled vessels. This posterior chain is shown in 

 figure 19, and more completely in figure 30 for a late stage. 

 The subocular tubules of this series appear most constantly 

 in injections of the jugular lymphatic from the time that it 

 reaches the distal extremity of the temporal region (fig. 6). 

 From the first they branch (fig. 13) and in the later stages 

 form extensive ramifications in the orbit below the eye (figs. 

 14, 18, 19, 30). Hoyer ('34) points out that these outgrowths 

 from the temporal sinus may be found in the adult frog. 



The process of centrifugal growth studied in early phases 

 in the previous period (see figs. 4, 5, 6 and accompanying text) 

 is thus carried to the periphery in the ventral area; and the 

 first lymph vessels to be found in the submaxillary region are 

 now demonstrated by injection of the jugular lymphatic. Un- 

 fortunately, however, only a limited number of injections of 

 the lymph vessels of the area are available, and these are 

 uneven in character. Hence, selection of specimens must be 

 made with caution to insure a reliable injection, at the same 

 time consistent in character with others of the series in later 

 as well as early stages. 



