MONOGRAPH OF THE EXISTING CRINOIDS. 397 



nucleus and cytoplasm, respectivelj', has already been noted. This variation is 

 also of interest in another connection. The progressively increasing staining 

 capacity of the cytoplasm which preceded yolk formation may be assumed to be 

 due to the gradual accumulation in the cytoplasm of material destined to be 

 utilized later in the formation of the definite yolk spherules. The variation in 

 the staining capacity of the cytoplasm in the fixed material would depend on 

 the capacity of the reagent employed to fix these metaplastic substances. They 

 are, as we should expect, well fixed in sublimate material, and almost as well fixed 

 in sublimate acetic material. In acetic bichromate material, on the other hand, 

 they appear to remain wholly unfixed and are washed out of the cell subsequent 

 to fixation. 



This varying action of the fixing reagent is accompanied not only by a corre- 

 sponding variation in the staining capacity of the fixed cytoplasm, but also in its 

 structural appearance. Thus in sublimate material, in which the basophile reaction 

 is most strongly marked, the cytoplasm has the appearance of being composed of 

 indefinite, closely packed, and in the earlier stages faintly staining, spherules. 

 In material fixed with an acid reagent, on the other hand, the texture of the 

 cytoplasm is that of a more or less open, fine, and deeply stained reticulum the 

 strands of which are, however, so fine that the cytoplasm as a whole does not 

 appear deeply stained. This reticular structui-e of the cytoplasm is found equally 

 in material fixed with acetic bichi-omate, with which reagent the basophile reaction 

 is almost, if not entirely, wanting. Such a beha\dor of the cytoplasm would seem 

 to suggest that the reticulum shown after fixation with an acid reagent represents 

 the living protoplasm of the original cytoplasm, from which the more or less 

 unfixed metaplastic substances have been washed out subsequent to fixation. 



In the adult egg the yolk consists of closely crowded spherules of two kinds — 

 the yolk spherules proper, constituting the greater bulk of the cytoplasm, and 

 the spherules which Professor Chubb calls the peripheral spherules, forming only 

 a thin layer at the periphery of the egg. 



Tlie yolk spherules proper average from 1 pi to 1.5 (jl in diameter and are always 

 quite spherical in form. After fixation with sublimate or sublimate acetic they 

 remain unstained by the hcematoxylin and appear pale yellow in color and re- 

 fringent. After fixation with acetic bichromate, on the other hand, the yolk 

 spherules are deeply basophile. prolonged extraction only serving to de.stain their 

 extreme peripheral portions. After fixation with Hermann's fluid, the spherules 

 remain unstained, are nonrefringent, and vary in color from a pale yellow to 

 a dark brown or even black. This coloration is due to the osmic acid in the fix- 

 ing reagent and is entirely independent of staining or extraction, a fact which, 

 together with their varying and irregular distribution, serves sharply to distinguish 

 them from the peripheral spherules. 



The peripheral spherules foi'm a thin layer immediately within the vitelline 

 membrane. The surface of the adult egg, and with it the inner surface of the 

 egg membrane, is, in fixed material. almo.st invariably thron^Ti into fine wrinkles, 

 the peripheral granules being collected in the ridges so produced. In tiie j-ounger 



