PLATE 6 



EYPLAXATIOX OF FIGURES 



12, 13, 14 From tliree saccessive .sections of a chick einbryo of (i days 

 and 16 hours, 13.5 mm. (series no. 42(i: slide XII. sections 9, 10 and 11). Photo- 

 micrographs, X 350. 



In figure 13 the arrow (/?) points to a lymph space in the mesenchyme. At 

 its right side the lymph space is seen clearly to open into the adjacent mesenchy- 

 mal intercellular spaces. The preceding section in the series (fig. 12) shows no 

 space (the arrow points to the same locality as in fig. 13). In figure 14 the arrow 

 points to a light area in the mesenchyme which represents the opening of the space 

 of figure 13 into the adjacent mesenchymal intercellular spaces; this can be seen 

 much more clearly with the microscope by changing the focus. The lymph space 

 shown in figure 13 is the same one represented in figure 20. 17 at the right of the 

 aorta. Aorta. /; celom (abdominal cavity), 23. 



174 



