398 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



eggs this surface wrinkling is absent, and here the peripheral spherules form an 

 even layer. 



The peripheral spherules of the adult egg differ from those of the rest of 

 the yolk both in their size and in their staining reactions. Their size, though 

 averaging that of the yolk spherules, shows a considerably greater range of vari- 

 ation, spherules measuring as much as 3 y. across being occasionally met with. 

 Their staining reaction, unlike that of the yolk spherules, shows no relation what- 

 ever to the mode of fixation, the spherules, after all reagents, being intensely 

 stained with iron haematoxylin. This staining reaction shows a further peculiarity, 

 for in all cases very slight differentiation is sufficient to destain these spherules 

 totally, and the ease with which this takes place is irrespective both of the nature 

 of the fixing reagent and the duration of its action. In sublimate, or sublimate 

 acetic, material with moderate extraction the deeply stained peripheral spherules 

 offer a striking contrast to the unstained yolk. With slightly greater extraction, 

 insufficient, however, appreciably to affect the appearance of the other cell elements, 

 the peripheral spherules are entirely destained, and they then appear as faintly 

 yellow spherules of about the same size as the yolk spherules, but, unlike these, 

 nonrefringent. In acetic bichromate material the peripheral layer can still be 

 detected, though the strongly basophile character of the yolk spherules after the 

 use of this reagent renders it much less conspicuous. Here again, however, slight 

 differentiation, to an extent which has no appreciable effect on the appearance of 

 the yolk, suffices totally to destain the peripheral spherules, which then form a 

 relatively clear region between the deeply stained yolk and the egg membrane. 



In Hermann material the peripheral spherules, when destained, can not be 

 distinguished from the faintly yellow and nonrefringent yolk spherules; but with 

 less differentiation they form with these as striking a contrast as in sublimate 

 or sublimate acetic material. Occasionally, however, in the Hermann material, 

 this contrast between the peripheral spherules and those of the rest of the yolk 

 is more or less obscured by the arrangement of the more deeply colored yolk 

 spherules. The destaining of the peripheral spherules is so sudden that, unless 

 differentiation is carried out under the microscope, it is rare to obtain slides in 

 which the peripheral layer is only partially destained. When, however, such a 

 slide is obtained, it is seen that nearly all the still visible spherules are as large 

 and as deeply stained as in less extracted slides, though present in far fewer 

 numbers. Only here and there will a spherule have been caught in the act of 

 destaining, and then it is seen that, even in the case of the individual spherule, 

 there is no gradual transition from an unstained to a deeply stained condition, 

 for a part of the spherule still remains as deeply stained as before, while the rest, 

 usually one side or the periphery, rarely the center, is already completely destained. 

 There is no evidence, in the destaining of the peripheral layer during differen- 

 tiation, that the more or less peripheral position of the spherules in any way 

 influences the ease with which they part with the basic stain. 



That the behavior of the peripheral spherules is not due merely to their 

 peripheral position is also indicated by the fact that in the adult egg they are 

 never so closely crowded as totally to exclude the ordinary yolk spherules from 



