250 ALICE THING 



outer layer seemed continuous with those of the inner layer yet 

 the line of demarcation between the layers was in no wa}^ obliter- 

 ated. The difference in the nature of the layers apparently is 

 one simply of refraction since there is no distinct structure divid- 

 ing them nor indeed any distinguishable boundary line. The 

 presence of an egg or yolk membrane which might have been 

 represented by a sharp line of demarcation between the striated 

 layer and the oocyte in figure 7 cannot be confirmed in tangential 

 sections. The boundary line (fig. 7) seems to be produced by 

 thickenings of the ends of cell prolongations at the points where 

 they reach the yolk. No trace of an egg membrane can be dis- 

 covered in the living oocj^tes of A. odoratus. 



Stage 3. The inner layer of the zona pellucida grows in thick- 

 ness comparatively slowly whereas the outer, increasing more 

 rapidly, becomes two or three times as thick as the former (figs. 

 9 and 10). The area of proHferation often stains very deeply 

 (fig. 9, a.p.) so that a densely colored belt borders the surface of 

 the outer layer remote from the yolk. At certain points in the 

 outer layer (fig. 9) are seen cross sections of the canals (c.) with 

 their contents (pr.) at other points a real striation, the result of 

 rows of granular filaments in continuity with identical rows of 

 filaments in the striated layer. This confirms the observation 

 made on living eggs in which was noted the presence of striation 

 in the outer la^^er. - When the area of proliferation has chanced 

 to stain less deeply one can see that the filaments are actually 

 prolongations extending down from the scanty cytoplasm sur- 

 rounding the epithelial nuclei into the substance of fhe zona 

 (figs. 10, 11, pr.) There are no indications that these filaments 

 branch as Retzius has reported in the case of the rabbit oocyte 

 but the small conical or knob-hke bases described by him appear 

 (figs. 9, 10, k.e.) as enlargements of the prolongations. Among 

 the granular filaments within the striated layer there appear more 

 homogeneous elements in continuity with the meshes of the 

 fundamental substance of the outer layer (figs. 9, 10, 12, /.s.). 

 In this stage the constituents of the zona are shown to be the same 

 as in stage 2 : a system of clear openings, cross sections of cyhnders 

 (c.) with their contents the prolongations (pr.) of the epithelial 



