1896.] 



Embryology. 



773 



7. The second and fourth grooves start from the periphery and move 

 toward the pole. 



8. The blastomeres are more rounded and the segmentation furrows 

 are deeper than those in most frog's eggs. 



9. The development is very rapid ; gastrulation begins within twelve 

 hours, and the tadpole escapes from the egg during the second or third 

 day. — Charles B. Wilson. 



Explanation of Plate I. 

 All figures drawn with Zeiss Camera x 16 diam. 



Figs. 1-4. Successive stages in cleavage of living egg at intervals of 



3 mins., 3 mins., 2 mins. 



Figs. 5, 6. Stages in cleavage of second living egg. 



Figs. 7-9. Stages in cleavage of third living egg — intervals, 2 mins., 



4 mins. 



Figs. 10-15. Stages in cleavage of fourth living egg — intervals, 2, 6, 



3, 4, and 5 mins. 

 Figs. 16-18. Stages in second cleavage of third egg. 

 Figs. 19, 20. Variations in second cleavage. 

 Fig. 21. Eight-cell stage of first egg. 

 Figs. 22-24. Stages in third cleavage of second egg. 

 Figs. 25-27. Variations in sixteen-cell stage. 



Explanation of Plate 11. 

 All figures drawn w4th Zeiss Camera. 



Figs. 28-30. First cleavage under higher magnification to show 

 rounded blastomeres. 



Figs. 31, 32. Beginning of first cleavage, showing radiating wrinkles 

 at pigmented pole. 



Figs. 33-35. Variations in wrinkles on the first furrow. 



Fig. 36. View of an egg during the fourth cleavage. 



Fig. 37. The same egg four minutes later. 



Fig. 38. Fusion and partial disappearance of the first groove. 



Fig. 39. Horizontal section of an egg during the first segmenta- 

 tion, taken at the level of the bottom of the furrow. 

 Nuclei added from the fourth section below this. 



Fig. 40. A portion of the same furrow about half way between 

 its bottom and the surface of the egg, more highly 

 magnified. 



Reprinted from The American Naturalist, September 1st, 1896. 



