254 BUMPUS, 



EXPLANATION OF PLATE XV. 



Fig. I. Chromatin granules from the "nebulse " in the region of the procephalic 

 lobes. X 1400. 



Fig. 2. Surface and side view of ectoderm cells, showing the relation of the ecto- 

 derm to the " yolk-pyramids." X 200. 



Fig. 3. Surface view of egg in stage H, seen from the dorsal side. X 60. The 

 deeper lying yolk masses may be seen through the transparent ectoderm. Chromatin 

 nebulre are shown at Cn. 



Fig. 4. Same as Fig. 3, seen from the ventral side. In Figs. 3 and 4 the nuclei 

 have been placed by means of a camera. 



Fig. 5. Transverse section through blastopore as shown in Fig. 4, 5—5. X 200. 

 The entodermal cells are colored a lighter shade of gray. 



Fig. 6. Transverse section through the plane 6—6 of Fig. 4. X 200. The 

 ectodermal cells are of a deep gray color. The yolk is represented in yellow. 



Fig. 7. Longitudinal section through the median plane of Fig. 4. X 200. Ecto- 

 derm represented in gray. The dark-colored patches extending to the left of the 

 entodermal mass are too deeply shaded, and their limits are too definite. 



