174 OTTO FREDERIC KAMPMEIER 



In 6 and 7 mm. larvae, the collateral tributaries of consecutive 

 intersegmental veins tend to anastomose with one another and 

 give rise to a longitudinal channel near the upper border of the 

 muscle somites. It is along this vessel that the dorsal or supe- 

 rior lateral lymph duct originates. It is formed by the fusion 

 of several discontinuous anlagen which evidently are engendered 

 by the attendant vein. Figures 16 to 25 inclusive, drawn from 

 sections of a 6 mm. embryo, reveal in detail the character of such 

 an anlage situated in the posterior half of the trunk, thus far 

 removed from the anterior lymph heart. A comparison of these 

 sketches with figure 15 will show that topographically this rudi- 

 ment lies in the pathway ultimately occupied by the completed 

 duct. It begins bhndly and it ends blindly. It is relatively 

 long, extending through forty-six sections. It is closely applied 

 to the venous wall throughout by far the major part of its course. 

 In figure 16 its anterior tip (I.) is indicated some distance dorsad 

 of the intersegmental vein (i.v.), but seven sections distally the 

 vein has approached the lymphatic (I., fig. 17) by bending up- 

 ward and backward. After two additional sections the vessels 

 are in contact (fig. 18), and it is impossible to discern a boundary 

 line between their adjoining walls. During the remainder of 

 its course the lymphatic anlage remains attached to the venous 

 intima. Four sections back of the level represented in figure 18, 

 it {L, fig. 19) appears on the side of the vein (i.v.) as a lump 

 solidly packed with yolk spheres, and as such it continues for 

 five or six sections. In figure 20 the lumen of the anlage (l.) 

 is bisected by a broad protoplasmic partition containing a nucleus 

 and a yolk corpuscle. In the ten following sections, one of which 

 is illustrated in figure 21, a similar condition prevails. Passing 

 over fourteen further sections, we meet with a sprout (fig. 22) 

 which is given off dorsally by the lymphatic anlage (L), but 



complex situated laterally are not straight uniform longitudinal channels through- 

 out their course, since either one at times bends around the pronephric duct, 

 fuses with the other on the opposite side for a short distance, then again becomes 

 independent and resumes its former position. Thus the separation of the post- 

 cardinal vein into a medial and a lateral division is a more or less arbitrary one, 

 here instituted for the sake of convenience and clearness in the descriptions. 



