70NA PELLUCIDA TN TURTLE EGGS 239 



Flemming ('82), Retzius ('89), Paladino ('90), Von Ebner 

 ('00), and Fischer ('05) affirm that the zona pelhicida is formed 

 of cytoplasmic prolongations of the epithelial cells. Flemming 

 describes fibers which "may be protoplasmic connections of the 

 egg cell with its neighboring cells; in the spaces between these 

 bridges the intermediary mass of the zona, gradually becoming 

 firmer, may be laid down." Retzius states that in the rabbit 

 cyhndrical cells send out branched processes which gradually 

 interlace so that a thick network originates around the egg. A 

 consolidation occurs on the inner belt of this network forming 

 the zona pelhicida. In the completely developed zona pellucida 

 the outer zone is also consolidated and between the inner zone 

 and the surface of the egg radiating striations can be recognized. 

 These represent granular filaments, which bore through the sub- 

 stance of the zona and are attached to the egg surface by small 

 conical basee. In the opinion of Paladino, bridges exist in the 

 rabbit between the epithelial cells as a whole, as well as between 

 these and the egg cell. In ripe eggs a fiber net exists between 

 the epithelium and the outer surface of the egg, the inner meshes 

 of which contain finely granular substance. Paladino gave a 

 rather bizarre interpretation of this granular substance, regard- 

 ing it as nutrient material derived from the breaking down of the 

 epithelial cells formerly existing in these areas. A true zona 

 pellucida is evolved from this substance which becomes hyalin 

 in character and strongly refractive. Von Ebner substantiates 

 in general the statements of Flemming and Retzius. The first 

 anlage of the zona shows a network closely attached to the egg 

 surface ; this gradually moves back toward the epithelium leaving 

 radiating filaments in connection with the egg surface to give 

 place to the "secondary zona substance." According to Fischer 

 the zona pellucida arises from unbranched cytoplasmic prolonga- 

 tions of the epithelial cells interwoven and pressed together. 

 Compression occurs to such an extent on the inner portion of the 

 zona as to eliminate the individual outlines and thus form a 

 homogeneous substance. In the completely developed zona 

 pellucida he distinguishes three layers, spongy, radiating and 

 homogeneous, of which the last named is the oldest and firmest. 



