2g8 KING. [Vol. XVII. 



belong to the o^^g, as they are a part of the inner and peritoneal 

 epithelium of the ovary and are never found around an egg 

 taken from the body cavity. 



The third egg-membrane, the " Chorion " of van Bambeke 

 ('80), the "Dotterhaut" of Schultze, and the •* Zona pellucida " 

 of Fick, arises apparently from the follicle epithelium. It has a 

 thickness of about 2 ^ and is seemingly structureless (Fig. 2, 

 ZP). Various writers, Joly ('72), Robin ('74), Stieda ('75), and 

 Schultze, have asserted that the Chorion is the only true mem- 

 brane belonging to the amphibian ^gg. Schultze, however, 

 finds between this membrane and the ^gg a narrow zone which 

 shows fine striations. He suggests for this zone the name 

 " Zona radiata," and considers it to be the peripheral yolk- 

 layer of the egg, and not a membrane in any sense of the 

 word. Fick, on the other hand, has stated that in eggs taken 

 from the body cavity there is a distinct inner yolk-membrane 

 beneath the Zona pellucida, which is not found in younger 

 eggs. 



The ovarian ^gg of Bufo has a distinct Zona radiata which, 

 with the combination stain I have used, colors a pale blue with 

 darker striations, and stands out in sharp contrast to the deep 

 blue Zona pellucida above it and the brown pigment layer 

 below (Fig, 2, ZR). Although at this stage the Zona radiata 

 can hardly be considered a real membrane, and is, apparently, 

 but the "ausserste kornchenfreie Dotterschicht," as Schultze 

 believes, I am inclined to consider it the beginning of the 

 inner yolk-membrane described by Fick. When the first 

 polar spindle is formed, the pigment layer comes to the ex- 

 treme edge of the ^gg, and there is no sign of a striated zone 

 above it. In favorable sections, however, there is distinctly 

 visible a thin, faintly staining, apparently homogeneous mem- 

 brane (PI. XXX, Figs. 35, 36), which is sometimes separated 

 from the surface of the ^gg and closely attached to the Zona 

 pellucida above it. 



In proportion to its size, the ^gg of Bufo is probably as 

 deeply pigmented as are any of the amphibian eggs. Individ- 

 ual eggs vary greatly in the amount of pigment they contain ; 

 but, in all cases, there is a thick layer of compact pigment 



