170 OTTO FREDERIC KAMPMEIER 



generally large and lie closely crowded in the cytoplasm. De- 

 pendent apparently on the degree of development, these cell 

 aggregations present somewhat different characteristics Some 

 have the form of a bulging compact local swelling of the venous 

 wall and can be pursued through a few sections only. Others 

 are quite as short in extent but manifest one or several small 

 crevice-hke cavities which it appears never open into the lumen 

 of the parent vein. Still others, older doubtlessly, exist as 

 comparatively long yolk-stuffed sprouts, one end of which adheres 

 to the bloodvessel and the other lies some distance aloof among 

 the thinly scattered large mesenchymal cells. Such growths, 

 at this time, are solid cell cords for the greater part of their course, 

 but betwcBU the masses of yolk ill-defined and irregular vacuities 

 now and then occur which intimate an intracellular origin. 

 Solely superficial differences, if any, can be detected between the 

 nuclei of the lymphatic endothelial buds and those of the mesen- 

 chyme. The former seem to be denser in chromatic substance, 

 although this is by no means diagnostic, for in this regard much 

 variation has been found among nuclei according to the mitotic 

 phase active at the time of fixation. A difference which may be 

 more pronounced, yet a difference which after all is neither causal 

 nor specific but is secondary, is the more frequent occurrence 

 in endothelial nuclei of an indented periphery due evidently to 

 the pressure of the yolk spheroids upon the nuclear membrane. 

 As has been and will be emphasized again, the character which 

 visibly differentiates the endothelial from the mesenchymal 

 cell in the early genetic stages of the cephahc region is the pres- 

 ence of much yolk. From this it is obvious that were both tissues 

 devoid of yolk it would scarcely be possible to follow the incipient 

 lymphatics through the meshwork of mesenchyme; and even 

 though all the details of their formation were known the seasoned 

 observer would suffer considerable perplexity in locahzing and 

 tracing them. On the contrary, with a large quantity of yolk 

 present in one of these two tissues and absent in the other, the 

 lymphatic anlagen, after they have been once recognized as such, 

 can be pursued from section to section with exceeding ease. In 

 the sections stained with hematoxylin and orange G the contrast 



