1 76 GARDINER. 



EXPLANATION OF PLATE XI. 



Fig. 21. Diagram of the thirty-eight-celled stage. The cells on the farther 

 side indicated by dotted lines. 



Fig. 22. Sixty-six-celled stage. 



Fig. 23. Longitudinal section through the four-celled stage. Showing the 

 segmentation cavity, S. 



Fig. 24. The same as Fig. 23 during the resting stage. Showing the seg- 

 mentation cavity obliterated. 



Fig. 25. Longitudinal section through the ten-celled stage. Showing the 

 segmentation cavity, S. 



Fig. 26. Diagram of the sixty-six-celled stage. The cells on the farther side 

 indicated by dotted lines. 



I. The remnants of the original blastomeres which form the mesentoderm. 

 II. The lineal descendants of cells B and B'. 



III. The lineal descendants of cell C and C. 



IV. The lineal descendants of cell D. 

 V. The lineal descendants of cell E. 



VI. The lineal descendants of cell D'. 

 VII. The lineal descendants of cell E'. 



Fig. 27. Longitudinal section through the ten-celled stage. Showing the 

 segmentation cavity filled up by A and A' . 



Fig. 28. Horizontal section through the sixteen-celled stage. 



Fig. 29. Cross section through the sixteen-celled stage. 



Fig. 30. Horizontal section through the twenty-six-celled stage. 



Fig. 31. An ovum cut from the adult. Showing the first cleavage spindle. 



Fig. 32. Pigment granules from an ovum of Polychaerus caudatus. 



Fig. 33. Section through an ovum much more advanced than the sixty-six- 

 celled stage. 



Fig. 34. Section through an ovum still older than that in Fig. 33. 



Fig. 35. Horizontal section through a ciliated embryo. 



