273 T, IWAKAWA. 



patches to that of the most minute granule that we are ahle 

 to recognise. 



Seen by reflected light these masses of yolk-spherules 

 appear whitish. These patches are found at a little later 

 date scattered throughout the peripheral portion of the 

 ovum, but a little larger and more closely arranged on that 

 side of the ovum where they presumably first appeared 

 than on the opposite side, as seen in fig. 22. 



In this section of an ovum, measuring "57 mm. in dia- 

 meter, and hardened in picro-sulphuric acid, the yolk 

 patches present an appearance quite different from that 

 which they have when examined in a fresh condition. The 

 fine granular protoplasm here appears darker than the 

 patches themselves — ^just the reverse of what is seen in the 

 living egg. The size of the spherules is now '002 to '003 

 mm. In fig. 21, which represents an optical section of a 

 portion of an ovum measuring a little less than 1 mm., ex- 

 amined in a fresh condition, some of the aggregations appear 

 to be more or less elongated in a radial direction. The further 

 history of these deutoplasmic masses can be learned only by 

 the study of sections of hardened ova ; the protoplasm stains 

 deeply red in picro-carmine, and the same is true of the 

 narrow boundary lines between the radially elongated masses 

 of yolk-spherules. The deutoplasmic elements and the proto- 

 plasmic matrix are thus well defined by the action of the 

 staining fluid. The persistence of the bounding lines even 

 after the greater portion of the ovum has become thickly 

 crowded with yolk-spherules is quite remarkable, and I am 

 not aware that such a feature has been described before. 

 That it is not an artificial product is perfectly certain, for I 

 constantly meet with it in eggs varying in size between '5 

 mm. and 1 mm., and meet with it in all phases intermediate 

 between figs. 20 and 23, and between fig. 23 and later stages 

 of complete obliteration. 



The disappearance of these radial bounding lines occurs 

 soon after the egg has attained a diameter of 1 mm., some 

 time before the yolk masses have reached, in their inward 

 growth, that stratum of protoplasm which lies next to the 

 germinal vesicle. The latter event is usually accomplished 

 by the time the ovum has attained a diameter of 1*5 mm. 



That these young yolk-spherules are not cells is of course 

 quite certain. 



That they originate loithin the protoplasm is proved by 

 the fact that there is always a cortical zone entirely free 

 from them, and that no such corpuscles are to be found at 

 any time outside the protoplasm. That they arise in the 



