THE EMBRYOLOGY OF THE HONEY BEE 129 



at subsequent stages, and has the appearance of being stretched 

 laterally. This is especially marked in the preparation from 

 which figures 48B and C were drawn. 



The cells of the primitive swellings only in part retain the 

 prismatic form seen at Stage VII; many of them are now seen to 

 be either in the act of division or to have recently divided. 

 These cells, fall into two classes, according to their position or to 

 their mode of division. First there are those in which the division 

 is equal, the mitotic spindle lying near and parallel to the external 

 surface and the resulting daughter cells occupying a superficial 

 position. These cells (Dbl) correspond to the "dermatoblasts" of 

 Wheeler and are destined to form hypodermis only. Second, 

 there are cells in which the division is unequal, the spindle lying 

 near the internal surface and usually directed at right angles to 

 it, the products of division consisting of a smaller central and a 

 larger peripheral cell. The larger cells in these pairs corres- 

 pond to the "neuroblasts" (Fig. 48B and C, Nbl) the smaller to 

 the "ganglion cells" of Wheeler. A difference in the arrangement 

 of the products of the dermatoblasts and neuroblasts becomes at 

 once evident; those of the dermablasts form ordinary epithelial 

 cells lying side by side; on the other hand each neuroblast to- 

 gether with its daughter cells form a compact and more or less 

 ovoid nest or mass of cells (Fig. 48B and C). 



At Stage IX, (Fig. 48D and 49A) the neural groove is both 

 narrower and shallower than at the preceding stage, while at the 

 same time the median cord has become correspondingly narrower 

 and deeper, its cells resuming their characteristic long prismatic 

 form. In cross section the median cord now presents somewhat 

 the form of the letter V, its outer end forming the point, although 

 in fact it is more or less truncate or flattened and constitutes the 

 floor of the neural groove. The cells of the median cord are 

 therefore long tapering in form, their inner ends always being 

 wider than their outer. 



At this stage the neuroblasts and dermatoblasts have become 

 completely segregated from one another, so that each primitive 

 swelling is divided into an inner neurogenic layer composed of cell 

 nests, the lateral cord, made up of the neuroblasts and the gang- 

 lion cells, and an outer dermatogenic layer made up of the pro- 



