1S02.] Phenomena and Development of Fecundation. 305 



the female apparatus the two directive sp hens which 

 precede it. 



In the embryo sac, as explained above, one .-tap- shows the 

 nuclei disposed in two tetrads, one at the summit and the other 

 at the base. In the apical tetrad the nuclei which belong to 

 the synergidoe are formed by a horizontal division (figs. 13 

 and 44) and their attractive spheres, therefore, occupy their 

 lateral faces. The two other nuclei on the contrary are orig- 

 inated in a perpendicular plane (fig. 43). Thus the nucleus 

 which goes to form the oosphere, has its two attractive spheres 

 above it (figs. 41 and 45, l>) while the ether thai travels to the 

 centre of the embryo sac to fuse with a similar one from below, 

 has its attractive spheres below it. (Upper nucleus, fig. 44, c 



The male nucleus, which is strongly contracted in its \ assngo 

 into the egg cell, increases in size and forms what is qow 

 termed the male pronucleus which is preceded, it will be 

 remembered, by its two attractive spheres (fig. 45, d). The 

 contact first occurs between the attractive spheres. These 

 coalesce two by two, male sphere with female sphere (fig. 46). 

 They then separate from each other so as to allow the male 

 and female pronuclei to pass between them and fuse (fig. 47 

 and 48). The male pronucleus unites with the u nude pronu- 

 cleus and remains thus in contact but is clearly distinguisha- 

 ble until the first segmentation starts. In each couple, formed 

 by the union of male and female attractive spheres, tho fusion 

 takes place slowly. When thoroughly fused fecundation is 

 complete. The two new spheres thus formed will be the origin 

 of the poles of the first segmentation spindle. Before the first. 

 division they orient themselves in such a fashion that this 

 spindle will be parallel to the longitudinal axes of the egg 

 cell. It results, from these observations, that the phenomena of 

 fecundation consists not only in the copulation of two nuclei of 

 different sexual origin but also in the fusion of two protoplasmic 

 bodies of equally different origin. 



The process of fecundation in the sea urchin, explained 

 above from Foil, agrees chiefly with this. Differing only in 

 that the attractive sphere does not divide until it enters the egg. 



Polar Globules in Plants.— Unvc we now anything in the 



