458 MONTGOMERY. [Vol. XV. 



of the nucleolus may take place during the mitosis, and 

 probably does so. 



After the completion of the mitosis just described, each 

 daughter-nucleus, which now has the value of a germinal vesicle, 

 first passes through the spirem stage of the metaphasis and 

 then enters upon the stage of synapsis, namely, the nucleolus 

 has a more or less central position, and all the chromatin of the 

 nucleus becomes grouped immediately around it (Figs. 264-266, 

 270, 271, 278), the peripheral part of the nucleus being trans- 

 versed by only a few fine, unstaining strands of substance 

 (linin .■'). All intermediate grades between this and the preced- 

 ing stage of the nucleus may be found. This is not an artificial 

 appearance caused by the use of a particular preservative, since 

 it is equally demonstrable on preparations fixed with aqueous or 

 alcoholic corrosive sublimate, sublimate with acetic acid, Flem- 

 ming's fluid, and alcoholic solution of picric acid ; only after 

 the use of Perenyi's fluid is this arrangement of the chromatin 

 not found, but this fluid seems to be rather a poor one for most 

 cytological study. It cannot be an artefact, since this appear- 

 ance is found only in ova of a certain size but not in those 

 which are larger ; thus it cannot be produced by the resistance 

 offered by the cell membrane to the penetration of the fixa- 

 tives, since this membrane is much thicker in the larger ova. 

 This central arrangement of the chromatin then represents a 

 definite stage of the germinal vesicle concomitant with the 

 first appearance of yolk globules in the cytoplasm.^ So at this 

 point we may briefly describe the yolk development and then 

 return to the changes of the nucleolus. 



The yolk first arises in the cell during the stage just 

 described, that is, immediately after the conclusion of the spirem 

 stage of the metaphasis. It appears in the form of small glob- 

 ules {Yk. GL, Figs. 262-264, 266, 270, 271), most of which are 

 arranged close to the outer surface of the nuclear membrane, 

 the first globules rarely arising at a distance from the nucleus. 

 At this period they stain less deeply than later. The yolk 



1 This stage of synapsis (Moore) appears to be characteristic of the anaphase 

 of the last spermatogonic and spermatocytic division in all the higher animals, 

 and no doubt can any longer be expressed of its representing an artefact. 



