ORIGIN OF LYMPHATICS IN BUFO 167 



rior extremity and then to accompany the vein back a consider- 

 able distance, sometimes lying hard against it, at other times 

 slightly aloof from it, as displayed in the sketch, and finally 

 becoming a solid attenuated cell cord that ends freely in the 

 mesenchyme. The smaller sinus anlage, shown in the same sketch 

 (fig. 7), stands in similar relations to the vein, but it is less ex- 

 tensive than the other, less wide in diameter and discloses fewer 

 vacuoles. The two anlagen are strictly independent of one 

 another. Beyond their terminations several shorter anlagen 

 are met with which are essentially like those described. 



A circumscribed area on the right side of another 6 mm. larvae 

 is portrayed in the second drawing, figure 8. Medially a sinus 

 rudiment (l.l.) is inseparably attached to the intima of the 

 external jugular (j.d.) ; at least no visible boundary line can be de- 

 tected between the adjoining walls of the two structures. More- 

 over, the lumen of the lymphatic is bisected by a thin cytoplas- 

 mic filament which passes from the inner combined venous and 

 lymphatic wall to the free outer wall. After extending through 

 a number of sections in this manner, the anlage becomes de- 

 tached from the vein and pursues its way parallel to it alone 

 through the mesenchyme until it bends downward and comes in 

 touch with another lymphatic undergoing development on the 

 ventral side of the vein. This is clearly set forth in figure 9, 

 where the anlage labelled l.S is approximated by anlage l.l, 

 which is identical with or, more correctly stated, a continuation 

 of the one (l.l) situated on the dextral wall of the blood channel 

 in figure 8. Eight sections, each 6 micra in thickness, intervene 

 between the two levels. The reader perceives that the lymphatic 

 rudiment (l.l) not only severs connection with the vein in this 

 short stretch, but it becomes broader and at the hinder level 

 (fig. 9) lacks a lumen in consequence of the large yolk corpuscles 

 that crowd every available nook and corner in it. This condition 

 is true of the greater part of its course. The rudiment 1.3 (fig. 

 9) is of brief length, appears behind the level represented in 

 figure 8 and possesses a large cavity proportionately, which, 

 separated from that of the bloodvessel (j.d.) merely by a thin 

 partition, resembles strikingly the extra-intimal spaces existing 



