MUSEUM OF COMPARATIVE ZOOLOGY. 201 



That portion of the interzonal filaments which falls within the polar 

 globule is gradually drawn into the thickenings ; at least the fila- 

 ments as such disappear. That portion which remains within the 

 vitellus, after suifering a diminution in thickness, probably disappears 

 altogether; so that shortly after the separation of the first polar globule 

 there is found in the vitellus only a single stellate figure near the ani- 

 mal pole. In the polar globule, on the other hand, there is no radiate 

 structure, — simply a group of prominent granules which are conspic- 

 uous from the readiness with which they are stained in carmine. 

 The globule often gives evidence of being limited by a special 

 membrane, which must have come from the envelope which we have 

 traced in its origin as a covering to the rising cone of the animal pole. 

 As that envelope was often thick at the apex and rapidly grew 

 thinner toward the base of the cone, so we find that the correspond- 

 ing structure is often much thickened at the distal extremity of the 

 globule (Fig. 22), — the point corresponding to the apex of the cone. 

 This thickened portion passes gradually into the envelope of the 

 sides and proximal face, which seldom shows more than a single contour 

 line. Before the complete detachment of the globule, there is formed 

 (Fig. 63), in the pedicel which still establishes a connection with the yolk, 

 at a point corresponding more or less closely with the equator of the 

 spindle, another thickening, which may be the equivalent of the cell- 

 plate {Zellplatte) of Strasburger. It is a disk of considerable thickness, 

 which extends quite across the pedicel, and is highly refractive. Though 

 not directly observed, it is reasonable to suppose that the final separa- 

 tion is along this disk, most likely by its division into two plates. 



The events which immediately follow the formation of the first polar 

 globule seem to me to have been less clearly treated by those who have 

 engaged in the study of the phenomena than any other portion of these 

 remarkable changes. Nor can I add much to their elucidation ; for it is 

 only after carefully comparing the results of my summer's work that I 

 am inclined to believe that there remains just here something of 

 a gap in the continuity of the best observations. It has been cus- 

 tomary for the second archiamphiaster to receive only a hasty de- 

 scription. Its origin has often been quite neglected. Because the result 

 in the case of both maturation spindles is the production of a polar 

 globule, the phenomena in the second case seem to have been considered 

 of only secondary value in the search for what is new. At the beginning 

 of this second stage careful attention is demanded to answer the ques- 

 tion, How does the second archiamphiaster arise 1 



