THE EMBRYOLOGY OF THE HONEY BEE 23 



the paternal, corresponding to the two pronuclei which unite to 

 form the first cleavage nucleus. 



A prominent and deeply stained mid-body is frequently ob- 

 servable between newly divided daughter nuclei (Fig. 8F). 



A peculiarity of mitosis, confined to the cleavage cells, at once 

 evident in glancing over the series represented in figs. 8A-H, is 

 the small size of the spindle as compared with that of the resting 

 nucleus. This disparity ceases to appear after the cells have 

 attained the cortical layer and commenced to form blastoderm. 



Multipolar spindles, as described by Lecaillon (1897a) were 

 not observed during cleavage, but in certain preparations, irregu- 

 lar mitotic figures were visible of the type represented by figure 

 8G. These are so rare, however, that it would not be permissible 

 to conclude that they are normal phenomena. 



In a number of insect eggs, 5 it has been observed that the 

 division of the cleavage cells take place in a definite direction, 

 that is, at right angles to the egg's surface. Examination of 

 sections of the bee's egg during Stages I and III, shows in di- 

 viding cells mitotic spindles turned in various directions and 

 apparently not conforming to any rule, except when the cells are 

 approaching the periphery of the egg. In this case the spindles 

 are more frequently parallel to the surface, indicating that the 

 resulting division plane will be normal to the surface. Never- 

 theless, a consideration of the relation of the cleavage cells to 

 one another will make it evident that the majority of the di- 

 visions must be in effect at right angles to the egg's surface, 

 since the cleavage cells — with the exception of those few destined 

 to form yolk cells, — are arranged in a single layer, and this for- 

 mation is maintained throughout the period of cleavage. The 

 products of every division — with the exception just noted — must 

 therefore eventually come to lie in this layer, so that whatever 

 the directions of the mitotic spindle may be, the plane ultimately 

 separating the daughter cells will be normal to the egg's surface. 



In figures 5, 6, and 7B there is observable a marked. contrast be- 

 tween the structure of the egg within the zone of cleavage cells 

 and that outside of it. This difference concerns the protoplasmic 

 meshwork. On the outside of the zone it is evident that the 



5 E.g., Aphis, Musca, Blochmann (1887); Bhtta, Wheeler (1889); 

 Forficula, Heymons (1895) ; Clytra, Lecaillon (1897a). 



