THE EMBRYOLOGY OF THE HONEY BEE 29 



less granular than the deeper lying portions, although it, in turn, 

 is still less transparent and darker than the protoplasm of which 

 the cortical layer is composed, and sharply marked off from it. 

 In figure 11F the migration is nearly completed; each cleavage 

 nucleus is embedded in a rounded swelling of the cortical layer, 

 and flanked on each side by a mass of cytoplasm derived from 

 the cleavage cell; these are united behind (centrad to) the 

 nucleus and merge with a still darker mass of cytoplasm which 

 still retains the branching and amoeboid form characteristic of 

 the cleavage cells. These irregular masses of dark cytoplasm be- 

 longing to adjacent cells now form a continuous although irregu- 

 lar stratum underlying the nuclei with their accompanying 

 cytoplasm. Next the cell boundaries become distinguishable, 

 faint indications of cell walls extending inwards from the bot- 

 tom of the furrows; the deeper stained bases of the blastoderm 

 cells are however still linked to one another, so that cell terri- 

 tories are yet not completely demarcated (Fig. 12A). Soon after, 

 the walls separating the cells are completed ; a delicate basement 

 membrane is formed near the bases of the cells, cutting off the 

 latter from the narrow inner zone of deeply staining protoplasm. 

 The cells are now completely delimited and the blastoderm, as 

 such, is established (Fig. 13A). It should, however, be always 

 borne in mind that these processes do not take place simultan- 

 eously over the entire surface of the egg, or even over any 

 extended part of it. They commence where the cleavage cells 

 first reach the cortical layer, namely, on the ventral side near 

 the anterior end, then extend rapidly over the entire anterior 

 third of the egg, thence progressing slowly caudad, so that all 

 phases of the process of blastoderm formation may frequently be 

 observed in a single egg. 



A striking feature of these early phases in the formation of the 

 blastoderm is the role played by the nucleus. As mentioned in 

 the section preceding, when the cleavage cells approach the corti- 

 cal layer, the nuclei take up a peripheral position in the cells. 

 This is plainly seen in figures 7 A and 11 A; the nuclei are now 

 very close to the external margin of the cell body. From this 

 point on the nucleus leads the advance into the cortical layer, 

 and after coming into contact with it (Fig. 11B) has apparently 

 become denuded on its peripheral side of cytoplasm belonging 



