CHAPTER 17 



Stratification of the egg granules 



a. Unfertilized Eggs. Plate VII 



The stratification of the well-centrifuged egg of Arbacia, beginning at 

 the light (centripetal) pole, is (i) oil, (2) clear layer without visible 

 granules (see Part IV, Clear Layer), (3) a thin finely granular layer of 

 mitochondria, (4) a large yellowish heavy layer of larger yolk granules, 

 (5) a red pigment layer at or near the (centrifugal) pole. The nucleus 

 is always at the centripetal pole just under the oil cap. (E. B. Harvey, 

 1932, 1936, etc.) (Plate VII, Photograph i and Figure 12). 



In the older work on Arbacia eggs, only four layers were described, 

 the mitochondrial layer being omitted, owing probably to insufficient 

 force (Lyon, 1906a, 1907; Morgan, 1909). In still earlier work on 

 Arbacia lixula, Sanzo (1904) obtained only two zones, a protoplasmic 

 and a granular zone, and he figures an oil cap; this led him to believe 

 that he had changed a homolecithal into a telolecithal egg. 



b. Vital Staining of Stratified Egg 



The diflferent layers of the centrifuged egg stain differently with 

 different vital dyes (E. B. Harvey, 1941c). A table is given (Table 8) 

 of a number of vital dyes and their effect on the different layers. Many 

 other stains were tried, especially acid dyes, without effect. Some dyes, 

 e.g., rose bengal, stained only after the egg was dead. The nucleus 

 does not stain, vitally, in any dye; and the cytoplasm only in basic 

 dyes as noted long ago by Mathews (1907). 



Quinine, cinchonine, and cinchonadine stain the pigment almost 

 black like methylene green, with no effect on development (E. B. H., 

 unpub.). 



c. Stained Sections of Stratified Eggs 



Eggs were fixed in Bouin's fluid, sectioned and stained with iron 

 hematoxylin; some were counterstained with eosin and orange G (E. 

 B. Harvey, 1940c). The clear protoplasmic layer which is optically 



