Katliarine Foot and E. C Stroboll 227 



in Photos. 13 and 100. Wc believe the ehroniatic granular substance 

 of the prophase (Photos'. 68 and 69) is the same as the chromatic gran- 

 ular substance of the metaphase (Photo. 99, Plate VI). These eggs were 

 killed in the same fixative, platino-osmic, and the substance can be recog- 

 nized at the two stages. In Photo. 100 the substance has a very different 

 distribution from that of Photo. 99, Plate VI, though the two eggs are at 

 exactly the same stage of development, i. e., metaphase of the first spindle. 

 In the chromo-acetic preparation (Photo. 100) the homogeneous achro- 

 matic cytoplasm is in the form of pronounced rays, combined in 

 such a way with the archoplasm that the latter may be interpreted 

 as cyto-microsomes. After some fixatives it certainly does assume 

 the form of cyto-microsomes and in these cases its identification as 

 a specific substance is possible only where it is accumulated into 

 dense masses. Its interpretation as a specific substance or as an 

 integral part of the cytoplasm depends upon its special manifesta- 

 tion after a given fixative and suggests that the opposing interpretations 

 are largely a question of terms. In this egg we claim its individuality 

 only on the ground that we think we can trace the substance with un- 

 broken continuity from its earliest aggregation as yolk nucleus in the 

 youngest oocytes to the cleavage stages — a large part of it contributing to 

 the formation of the polar rings. Aggregations of archoplasm not alone 

 in chromo-acetic preparations, but in corrosive sublimate and many 

 others are readily differentiated by double staining (Foot, '96), but this 

 method obscures its presence when it is most evenly distributed through- 

 out the egg, and for this reason study of comparative fixation has seemed 

 the more profitable method to follow (Foot and Strobell, '00) . When the 

 oocyte first order has reached its maximum growth it is especially diffi- 

 cult to differentiate the archoplasm. Its presence at this stage is demon- 

 strated in Photos. 68 and 69, Plate IV, and Photo. 10, Plate I, shows 

 an interesting segregation of the substance in the form of a " polar ring'' 

 which is not normal^ due until the pronuclear stage. This is a section 

 of an oocyte with the germinal vesicle intact and the chromosomes not 

 yet formed, a stage earlier than that shown in Photos. 68 and 69. There 

 is a similar aggregation of archoplasm at the opposite pole of this egg 

 and these two polar aggregations present a striking resemblance to many 

 polar rings of the pronuclear stages which are not invariably in the form 

 of a ring. This precocious polar segregation of the substance in Photo. 

 10 appears to us to demonstrate tlie presence of this definite substance 

 in the egg during these early stages and the granular appearance of the 

 archoplasm in this pliotograph is typical of all fixed material. The 

 chromatic centers of asters fail to show this granular effect (Photos. 84, 



