ZONA PELLUCIDA IN TURTLE EGGS 251 



cells and the mesh work of the cuticular fundamental substance 

 (f.s., fig. 12, o.L, i.L). In the inner layer the meshes of the funda- 

 mental subst^ance stand out more clearly than in figure 8 since 

 they are more deeply stained. Here the tubes and filaments have 

 increased greatly in length and the fundamental substance in 

 amount. In the series of stages showing thes^ elements in vari- 

 ous phases of development it can be noticed that whereas in 

 numerous openings the prolongations are very well seen in other 

 openings no contents are perceptible. The absence of prolonga- 

 tions from some spaces may be due first to imperfect fixation and 

 staining, secondly to the real lack of systems of cavities corre- 

 sponding to and overlying the intercellular spaces and conse- 

 quently the primitive terminal bars in the first stages of develop- 

 ment. A very thin discontinuous line between the knob-like 

 enlargements of the ends of the granular filaments and the yolk 

 substance in figure 9 may represent a real egg membrane. This 

 appearance is very rare and further investigation with more 

 refined methods is required to explain it. In tangential sections 

 one sees nothing convincing of the presence of an egg membrane. 

 It may be as Van Beneden asserts regarding the eggs of the rabbit 

 that it can never be isolated in ovarian eggs until a short time 

 before impregnation. In that case it could not be seen in turtles, 

 eggs as small as these which are at present being investigated. 



SUMMARY 



1. The epithelium surrounding the ovarian egg in all turtles 

 herein reported is represented by one layer of prismatic cells 

 between the sides of which short and long bridges extend. The 

 intercellular spaces at the surface of these cells are closed by a 

 special cement, the terminal bars. The cell is formed by a nucleus 

 and by cytoplasm consisting of an attraction sphere composed 

 of a central corpuscle, a medullary and a cortical layer. These 

 spheres form a dense endoplasm around the nucleus from which 

 filaments extend to a clear layer near the periphery, the exoplasm 

 in a delicate network. 



