J 64 RICHARD ASSHETON. 



Fig. 35. — Portion of a section of the embryonic disc of a rabbit of the 

 125th hour. The hypoblast here is seen as consisting of cells with very con- 

 spicuous central portion, but these are connected by fine and apparently dis- 

 continuous strands — really a network. X 465. 



PLATE 17. 

 Pig. 36. — Surface view of a portion of the embryonic area of a rabbit of 

 about the 150th hour. Prepared with nitrate of silver. This corresponds to 

 the sections Figs. 32 — 34. The shading is diagrammatic, and represents only 

 my interpretation of the areas as defined by the silver nitrate lines, which are 

 drawn by camera. 



Fig. 37. — A diagram of the embryonic area of the rabbit of the 96th hour. 



Fig. 38. — A diagram of the embryonic area of the rabbit of the 100th hour. 



Fig. 39. — A surface view of a portion of the wall of the blastodermic 

 vesicle of the rabbit of the 103rd hour. Seen from within. Preserved 

 Flemming ; stained borax carmine. X 350. 



Fig. 40. — A portion of the wall of the vesicle, showing the termination of 

 the inner layer at the 144th — 150th hours, x 350. 



Fig. 41. — A diagram to show the constancy of the angle subtended by the 

 inner mass during the earlier stages of the growth of the blastodermic vesicle. 



Fig. 42. — Camera drawings of the blastodermic vesicles of a rabbit of the 

 100th, 125th, 140th, and 175th hours, as seen from the side, arranged so as 

 to show the supposed variation in rate of expansion of the dififerent zones 

 under the influence of — (1) increase of hydrostatic pressure within ; (2) resist- 

 ance (mechanical) of cellular wall of vesicle and albuminous layer, which are 

 supposed to be nearly constant factors ; and (3) the vital activity of the cellular 

 wall of the vesicle, which by hypothesis is supposed to vary along certain 

 zones and areas. 



