430 OTTO F. KAMPMEIER 



later more specialized lymphatic endothelium. Synchronously, 

 the reoi'ganized approach becomes confluent with the contiguous 

 lymphatic spaces of the duct anlage by the breaking down of 

 tissue partitions and septa between them. The vestiges of the 

 old vascular intima may persist throughout a number of stages 

 clinging to the wall of the new cavity, but it gradually fades and 

 vanishes as the thoracic duct acquires more and more of its func- 

 tional activity. 



Histologically, all incipient lymphatic anlagen, whether they 

 are spaces independent in position or spaces following, transform- 

 ing and expanding the discarded pathways of redundant venous 

 channels, are decidedly different from either a ctive vein or a 

 mature lymphatic. They lack definition and possess vague and 

 undifferentiated outlines; for the cells of their walls are not 

 arranged in that end-to-end fashion so characteristic of vascular 

 endothelia. Instead, many instances were observed under strong 

 magnification where the tissue cells in their longest diameter 

 stand perpendicular to the periphery of the anlagen and project 

 far into the lumen with their cytoplasmic filaments, a condition 

 unquestionably brought about by the addition or fusion of con- 

 tiguous spaces. Figure 9, which is an accurate camera lucida 

 drawing of a highly enlarged portion of the area pictured in figure 

 8, should be carefully examined as depicting clearly the features 

 here mentioned. With the most critical observation one is not 

 able to detect differences at this stage between those cells con- 

 stituting the boundaries of the lymphatic anlagen (3a, b, c, d) and 

 those of the mesenchymal reticulum, either in regard to their 

 arrangement and shape or to their staining attributes. 



While there is sufficient evidence for the atrophy of veno- 

 lymphatics (6a, fig. 9) in their elimination from the blood stream 

 and the recession of their intima, further evidence is revealed at 

 this stage by their reaction to the stain. Treated with heama- 

 toxylin and orange-G, the defunct intima takes an opaque brownish 

 color as compared with the transparency of a functional vessel. 

 Their lumina also contain the debris of blood cells. That these 

 conditions are not induced by poor fixation is evinced by the nor- 

 mal appearance of the veins in the immediate vicinity. For 



