400 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



this region, ordinary yolk spherules occurring among the peripheral spherules 

 right up to the inner surface of the vitelline membrane. 



It is therefore clear, from a study of the evidence afforded by the adult egg 

 alone, that the peculiar behavior of the peripheral layer of spherules is not of the 

 nature of a fixation artifact, nor in any way due to the peripheral position which 

 they occup}'; it is, instead, evident that they must differ considerably in consti- 

 tution from the yolk spherules. Nor is there any evidence that a conversion of 

 the one into the other is taking place, a conclusion fully in harmony with the fact 

 that the number of the peripheral spherules remains fairly constant, not only 

 during the closing period of yolk formation, but also after the completion of this 

 process for as long as the egg remains in the pinnule. 



The vacuolated areas indicating commencing yolk formation remain unstained 

 after all fixing reagents, and in sublimate or sublimate acetic material they stand 

 out in strong contract to the intensely basophile cytoplasm. In acetic bichromate 

 material the yolk spherules do not acquire their (with this reagent) intensely 

 basophile character until some time after their first appearance. With Hermann's 

 fluid the vacuoles in the areas of commencing yolk formation can be seen on their 

 very first appearance as faintly yellow spherules standing out well against the pale 

 blue cytoplasm. 



Isolated groups of yolk spherules, of a size equaling those of the adult egg, are 

 frequently present long before yolk formation becomes general over the whole 

 cytoplasm. These isolated areas of precocious yolk formation show, however, no 

 constant spatial relation to any of the other cell elements, and as soon as yolk 

 formation becomes general this process proceeds most rapidly at the cell periphery, 

 and as it extends from without inward the interspherular substance, and with it 

 the basophile reaction of the cytoplasm, slowly disappear, the last traces forming 

 a faint and irregular perinuclear area of ever decreasing dimensions. 



In addition to this complete absence of any spatial relation between the yolk 

 nucleus and areas of commencing yolk formation, it should be noted that in the 

 earlier stages of this process the yolk nucleus still retains its regular form and 

 shows as yet none of the appearances which have been previously interpreted as 

 indications of its granular disintegration. Moreover, in later stages yolk for- 

 mation proceeds within the body of the yolk nucleus exactly as in other regions 

 of the cytoplasm. The only difference which the yolk nucleus shows from the 

 surrounding cytoplasm consists in the more intense staining reaction of the inter- 

 spherular protoplasm in this region, a reaction which renders the yolk nucleus 

 visible long after all tendency to retain the basic stain has disappeared from the 

 surrounding cytoplasm. In the later stages of yolk formation the faintly stained 

 and irregular yolk nucleus exactly resembles in appearance the still faintly baso- 

 phile perinuclear region of the cytoplasm, and in many cases only its peripheral 

 position serves to distinguish it from the latter region. 



As soon as yolk formation becomes general, the peripheral spherules make 

 their appearance. As always, they are intensely basophile, but at this early stage 

 they are extremely minute in size, far smaller than the yolk spherules, and are 

 scattered sparsely over the body of the cell. At a slightly later stage the spherules 



