122 



BERTRAM G. SMITH 



Immediately beneath the zona radiata hes a peripheral layer of 

 yolk-free cytoplasm, which from analogy with the teleost egg I 

 shall call the protoplasmic mantle.' In the region of the vegetal 

 pole this is so thin as to be barely recognizable with a magnifi- 

 cation of 500 diameters ; in the region of the animal pole it is thick- 

 ened to form a disc which I shall call the 'cytodisc' At the ani- 



cy. 



y.d. 



^:^•^ 











.^7 



N&^yi;^•>A;^.•:■%i^.V'->Vv■■■ ■ '-^ 



Fig. 24 Meridional section through an ovarian egg of an adult Cryptobranchus 

 allegheniensis killed Aug. 17. X 20. cy., cytodisc; y. d., yolk disc. 



mal pole the cytodisc reaches its maximum thickness of about 

 15)u- — a little thicker than the layer of follicle cells proper. 



The remainder of the egg is filled with yolk. Underlying the 

 cytodisc and occupying an area about 100° in diameter surround- 

 ing the animal pole, is a thick layer of fine but dense yolk which I 

 shall call the 'yolk disc' The cytodisc and yolk disc combined 



