258 BUMPUS. 



EXPLANATION OF PLATE XVII. 



Fig. i. Surface view of egg in same stage as represented on PI. XIV., Fig. J. 

 X60. 



Figs. 2-4. Transverse sections through the egg along the lines similarly desig- 

 nated in Fig. 1. X 200. The ectoderm is represented in gray. The mesoderm is 

 represented by the single layer of elongated nuclei which extends, immediately 

 under the ectoderm, from the median line to near the lateral limits of the section. 



Fig. 5. A longitudinal section through the median line of Fig. I. The contour, 

 due probably to the action of reagents, is somewhat too irregular. X 200. (The 

 lithographer has given too much shading to the yolk spheres in the lower, deeper 

 portion of the entodermal mass.) 



Fig. 6. A transverse section through the blastopore. X 400. 



