Plate VII. 



Fig. 50. This embryo shows the result of the operation described in Ex- 

 periment II (page 93). The injury was made on the posterior edge of 

 the dorsal lip, thirty-five and three-fourths hours after fertilization. The 

 egg was then incubated for forty-nine hours. The anterior end of the 

 embryo is normal in every way, and nineteen pairs of somites are devel- 

 oped. The depth to which it was necessary to focus the microscope in 

 order to obtain an image of the injured material in the entoderm can be 

 seen by the fact that the somites are out of focus, x 30. 



Fig. 51. A transverse section through the injured region of the preced- 

 ing embryo (Fig. 50, op). The affected cells lie in the entoderm, x 95 



Figs. 52, 53, and 55 are all from an unincubated blastoderm. Fig, 52 shows 

 the entoderm and part of the ectoderm above, and a "free nucleus" at n lying 

 on the floor of the cavity, which contains many small granules, x 688. 



Fig. 53. It shows two small nucleated cells (at s and s), which are 

 doubtless wandering entoderm cells. There are also ma^ny large yolk 

 masses in the cavity, x 500. 



Fig. 54. This shows the result of the operation in Experiment VI. The 

 injury was made thirty-five hours after fertilization, and the egg then incu- 

 bated for forty-eight hours. There are twelve pair of mesoblastic somites 

 present, the development being slightly retarded, x 20. 



Fig. 55. This shows a large multinucleated yolk mass, in which most of 

 the nuclei are degenerating, x 500. 



Fig. 56. This shows the result of the operation in Experiment X. The 

 injury was made on an unincubated blastoderm, and the egg was then incu- 

 bated for twenty-three hours. The embryo is normal in every way. X 25. 



