ORIGIN OF LYMPHATICS IN BUFO 177 



sinus anlagen, as well, resemble mesenchymal nuclei indistin- 

 guishably. What lends interest to the case is that the anlage is 

 exceedinglj' short, being limited to six sections, though its caliber 

 is proportionately broad. It ends as suddenly as it begins 

 (compare figs. 32 and 33 with 30). In its abrupt course it lies 

 adjacent to the vein (p.L), and at its posterior end (/., figs. 32 

 and 33) the two vessels are in contact but their lumina do not 

 communicate. Proceeding distally from this level, nothing is 

 encountered which might suggest a lymphatic anlage until 

 twenty-eight sections have been passed over, where another 

 similar endothelial-lined space exists in a similar position. 



Figures 34 and 35 illustrate a rudiment of the inferior lateral 

 lymph duct on the right side of another 6 mm. embryo. More 

 than fifty sections intervene between the anterior lymph heart 

 and the blind anlage (7.) pictured here. In all notable qualities 

 it is like the anlage described and figured last, except that it is 

 longer, extending through eighteen sections, and is larger in 

 circumference (fig. 34). Near its posterior limit it becomes 

 much compressed and flattened out against the venous intima 

 to which it is apparently firmly adherent (I., fig. 35). The 

 terminal portion, however, is not attached to the vein (p.L) 

 but lies slightly removed in the mesenchyme. 



The discontinuous anlagen described above are not isolated 

 cases; several such anlagen may be found in all 6 and 7 mm. 

 toad larvae, which are the critical genetic stages of the lateral 

 l^'mph ducts. In older 7 nmi. larvae these discrete lymph 

 vessel rudiments have elongated and by further increment and 

 by coalescence are creating continuous channels. Yet it is ex- 

 ceedingly interesting to note that the tips or ends of consecutive 

 anlagen do not always strike each other squarely; the writer 

 has frequently observed the posterior tip of one and the anterior 

 of another a considerable distance apart in the same section. In 

 other words, the anlagen in their growth and elongation had 

 shoved past one another without immediately meeting. Eventu- 

 ally they become confluent by the gemmation of lateral sprouts 

 or the dilatation of their lumina. This doubtlessly explains the 

 irregularity and sinuosity of their course at an early period after 



THE AMERICAN JOURNAI, OF ANATOMY, VOL. 17, NO. 2 



