640 INDEX. 



Yolk-cells : Frog, 104, 105, 146 



Yolk-plug: Frog, 107, 111, 147 



Yolk-sac: Chick, 222, 226; Rabbit, 367-369; Man, 476, 483, 496, 544 



Yolk-spheres : Hen, 230 



Yolk-stalk: Chick, 226; Itabbit, 399, 403; Man, 544, 548, 601, 602 



Zona pellucida : Man, 455 



Zona radiata : Rabbit, 348 ; Man, 453 



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