THE EMBRYOLOGY OF THE HONEY BEE 31 



to the body of the cleavage cell. That this migration is accomp- 

 lished by an actual movement on the part of the nucleus itself is 

 contrary to the facts of biology; the source of the movement 

 must therefore be referred to the cytoplasm, as Marshall and 

 Dernhehl have pointed out. Moreover, nuclei are frequently 

 seen elongated at right angles to the line of movement, as though 

 somewhat flattened by pressure before and behind (Figs. nD 

 and F). A flattening of the nuclei has also been observed to oc- 

 cur under similar circumstances by Lecaillon (iSg/a) in Clytra, 

 and by Noack (1901) in Musca, and is similarly explained by 

 these investigators. In these instances, however, the nuclei are 

 flattened only at their peripheral ends. 



A second feature to be noted is the sharp separation of the 

 protoplasm derived from the cell body and that of the cortical 

 layer. This separateness is readily seen in figure 12 A, when the 

 cell walls are beginning to appear. An ultimate fusion of the 

 material from these two sources occurs later, but seems to take 

 place only very slowly. The cytoplasm of the blastoderm cells 

 is therefore derived in part from the cleavage cells, but not all 

 of the cytoplasm from this source is thus employed, a consider- 

 able portion being temporarily cut off and left within the blasto- 

 derm in the form of a deeply stained granular layer, described 

 above. Such a layer of granular protoplasm was first observed 

 by Weismann (1863) m Musca and named by him the "innere 

 Keimhautblastem" ; this layer may then accordingly be termed 

 the inner cortical layer, but it must be remembered that it has 

 no close genetic relationship with the cortical layer proper. This 

 inner layer has subsequently been found to exist in the eggs of 

 many insects, but appears to be wanting in the orders Orthoptera 

 and Dermaptera. 



Figures 13 A and 136 represent transverse sections through an 

 egg just after the blastoderm has become established. As is 

 readily apparent, the blastoderm is not of uniform thickness 

 throughout, but is thinner on the dorsal than on the ventral side. 

 Comparing figure 136, from the posterior region of the egg, 

 with figure 13 A, through its anterior region, it is evident that 

 the blastoderm-forming cells of the posterior region are much 

 less numerous than those of the anterior region. This difference 

 is directly referable to the preceding cleavage stages when a 



