Plate IV. 



All the photographs in Plates IV-VI are from the sections of the blasto- 

 derms, and the prints were made directly from these negatives without 

 any retouching. The Zeiss apo., 8 and IG mm. lenses, and compensating 

 ocular 4 were used with camera draw varying from 12 to 20 inches. The 

 magnification is given in each case. 



All of the photographs in Plates VII-X were made directly either from 

 the whole mount preparations or from the sections, with various combina- 

 tions of lenses. In each case the magnification is given. 



Fig. 29. A median longitudinal section taken through CR of Fig. VI. 

 Note especially the gradual increase in the depth of the blastoderm in pass- 

 ing from the right (posterior) to left (anterior), x 143. 



Fig. 30. Longitudinal section taken slightly to the left of the line CD 

 of Fig. VII. The thiiming-out is farther advanced than in the preceding 

 section, and at the point marked "x" is clearly shown the cells that have 

 loosened and sunk down during fixation. Otherwise the subgermiual cavity 

 would contain only a few non-nucleated yolk masses, x H^- 



Fig. 31. An enlarged portion of the posterior end of the preceding pho- 

 tograph. X 301. 



Fig. 32. Posterior end of a section taken through plane x-x' of Fig. VIII. 

 See text for description, x 3G6. 



Fig. 33. Posterior end of a longitudinal section, seven sections to the 

 left of the median line, from a blastoderm taken thirty-four hours after 

 fertilization, or seven hours before laying. The anterior limit of the ento- 

 derm is shown at "e." x 1^3. 



Fig. 34. The median section of the same blastoderm as the preceding. 

 The length of the invaginated entoderm is necessarily greater than in Fig. 

 33. X 193. 



