456 



OTTO F. KAMPMEIER 



ing their genesis their walls are composed of the undifferentiated 

 mesenchymal cells (figs. 6, 9, 18, etc). We have also seen the 

 method of concentric addition of tissue spaces by which the 

 anlagen enlarge during the later transition and early lymphatic 

 stages, implying thus a continual shifting of their boundaries so 

 that an intima may be said to be temporarily established, replaced, 

 and reorganized a number of times (figs. 22, 25, etc.) Ultimately, 

 however, we can speak of a definite and permanent endothelium 



Fig. 26 Transverse section through the region of the cisterna chyli in a 23 mm. 

 pig embryo (series 67, slide 43, section 14), X 150. 5, anlage of the cisterna chyli 

 showing the indefinite and ragged outline of its cavity, the absence of a specialized 

 intima, and the addition of small spaces (4) from the mesenchyme; the vestiges 

 of the former veno-lymphatics have completely disappeared; 13, aorta; 14, sym- 

 pathetic nerve trunk. 



