THE EMBRYOLOGY OF THE HONEY BEE 19 



fourth to one-third of the length of the egg from the cephalic 

 pole. In some cases the cells appear as though concentrated on 

 this point, but its location is probably subject to considerable 

 individual variation. Soon after the first cells reach the surface 

 the anterior half of the egg becomes rapidly invested with a 

 covering of cells, yet the ventral surface is, as figures III and 7 A 

 show, generally attained a little before the dorsal. The attain- 

 ment of the periphery of the egg by the cleavage cells now pro- 

 gresses slowly caudad, the caudal pole itself being the last to 

 receive a cellular investment. 



By far the greater number of cells advance toward the peri- 

 phery in a single row, eventually attaining the cortical layer and 

 then forming blastoderm, nevertheless, a few linger behind 

 within the yolk and become the yolk cells. Three of these are 

 clearly seen in figure 7 A, YC. At this period they are not dis- 

 tinguishable from the other cells by any visible characteristics. 

 Their origin has already been correctly described by Dickel 

 (1904) for the honey bee, and conforms to that of the higher 

 insects in general. The further history of these cells will be 

 considered later. 



The varied and highly irregular amoeboid contour of the in- 

 dividual cleavage cells is illustrated by figures II, III, 6, /A and 

 B, as well as by the series represented in figures 8A-F. As the 

 figures show, the outline of the cell is indented by concavities ; 

 these concavities represent the spaces occupied by the vitelline 

 spheres. Between these concavities irregular slender processes 

 extend out from the cell ; these either merge with the protoplas- 

 mic network or unite with corresponding processes of adjacent 

 cells, so that the cleavage cells, together with the other proto- 

 plasm of the egg protoplasmic meshwork, cortical layer form a 

 single continuous whole, and in fact constitute a true syncitium. 3 

 As the cells move toward the surface they become more numer- 

 ous by repeated divisions, and more closely crowded together, 

 their connecting processes become correspondingly more numer- 

 ous, shorter, stouter and more regular in outline. Figure 9 il- 

 lustrates a tangential section through the layer of cleavage cells 

 near the anterior end of an egg between Stages II and III show- 

 ing the manner in which the cells are linked together at this time. 



d See footnote p. 16. 



