440 BULLETIN OF THE 



After the formation of the second polar globule, which somewhat ex- 

 ceeds the first in size, but is otherwise like, and formed like, the first 

 the half of the spindle remaining in the egg contains a disk of granules 

 and about its tip a homogeneous area and faint radial striations. A little 

 later a cluster of vacuoles closely pressed together has taken the place 

 of the granules of the disk. These vacuoles are sliarply limited from 

 the yolk by a dark lustrous rind having the appearance of nuclear sub- 

 stance, and in the contained fluid small dark granules are suspended. 

 The vacuoles soon increase in size, and flow together into a simple, lobed 

 body, — a nucleus. This female pronucleus migrates toward the centre 

 of the egg, where it meets the male pronucleus. Meanwhile there have 

 appeared in the last-formed polar globule numerous vacuoles in place of 

 the granular zone which occupied its middle. These enlarge and unite 

 into a single vacuole with a dark cortical layer, which stains in carmine. 

 The first-formed globule is partially constricted into two. All three 

 remain attached to each other, and, through the largest one, to the yolk, 

 till about the time of the first cleavage, when they are all combined into 

 a single flattened structure containing three bodies that stain readily. 

 The formation of each polar globule takes place in the manner of a cell 

 division, or, in view of the difference in size of the products, as a cell 

 budding. 



Hertwig's studies on Rana are mostly confirmatory of the results 

 reached by Van Bambeke. In the ovarian egg at the time the germi- 

 native vesicle is growing most rapidly it presents a spherical form and 

 complicated structure. There is a membrane and about a hundred 

 nucleoli, which are in contact with its inner surface,"^ and a rich net- 

 work of finer or broader bands of protoplasmic substance, whose function 

 it is to nourish the nucleoli. The latter are most important compo- 

 nents of the nucleus. Alread}^ at the beginning of winter the germina- 

 tive vesicle is found more or less displaced from the centre toward the 

 pigmented pole of the egg, and, although a shrinking in the vesicle 

 takes place, the cavity found outside the vesicle in eggs hardened in 



formation of the second polar globule and the first segmentation on the other hand, 

 are very nearly the same, so that the production of a " homogeneous nucleus " and its 

 conversion into a second spindle cannot be excluded on account of any lack of time 

 for the metamorphosis, provided the changes transpire with the same rapidity as they 

 do in the preparation for the first cleavage. 



* The nucleoli differ in chemical behavior from the nuclear membrane, with which 

 they do not become fused. In Hertwig's opinion, therefore. Van Beneden's view 

 that both are unaltered remnants of the primitive nucleus (i. e. ''nuclear essence") 

 is not tenable. 



