4IO 



EVCLESHVMER. 



EXPLANATION OF PLATE XVIIL 



All figures from Amblystoma pumtaUim. 



Fig. I. Egg with enclosing membranes just after laying (X8). 



Fig. 2. Superior hemisphere of egg 2 hrs. after laying, showing "light spot," 

 within which lies the first polar body (X 15)- 



Fig. 3. Superior hemisphere 4 hrs. after laying, showing eccentric aggregation 

 of pigment, also presence of second polar body (X 15). 



Figs. 4-12. Successive stages of cleavage from living egg (X 15). 



Figs. 13-18. Successive stages of cleavage in superior hemisphere of living 

 egg, showing order and time of appearance (X 15). Heavy black line indicates 

 the first cleavage ; heavy black broken line, second cleavage ; blue line, third 

 cleavage ; heavy red line, fourth cleavage ; black dotted line, fifth cleavage ; red 

 dotted line, sixth cleavage ; light black line, seventh cleavage. Numerals indicate 

 time of first appearance of the furrows. 



Fig. 19. Meridional section of egg in stage corresponding to Fig. 7, showing 

 early segmentation cavity (x 20). 



Fig. 20. Meridional section through the centers of least and most densely 

 pigmented areas in stage corresponding to Fig. 9 (X 30). 



Figs. 21, 22. Meridional sections through same areas, showing thickening of 

 roof in densely pigmented area, and thinning at opposite side (X 35, 40). 



