206 THE EMBRYOLOGY OF THE HONEY BEE 



Md 



Md 



FIG. 84. Transverse section through the cephalic region of an embryo, 

 Stage IX, intersecting the antennal rudiments (Ant) and their mesodermal 

 sacs (AntMesa). Ectoderm shown in outline only, x 243. 



continuous with the mesodermal tubes. The cavities of all of the 

 rudiments of the gnathal appendages are stuffed full of meso- 

 dermal cells, which in the first and second maxillary segments are 

 joined to the lateral strand on each side by a thin bridge of cells 

 (Fig. 67, Meso). 



The fate of the mesodermal elements of the head is briefly as 

 follows : The central part of the anterior mass of mesoderm 

 enveloping the stomadaeum becomes the layer of oesophageal 

 muscles. The remainder of this mass is consumed in the produc- 

 tion of those muscle strands which traverse the labrum and adja- 

 cent parts of the head capsule. The coelomic sacs of the antennal 

 segment, at first quite small (Fig. 84, AntMeso) expand rapidly 

 as the yolk is withdrawn from the head region and at Stage X 

 become thin walled sacs which nearly fill the posterior half of the 

 head capsule. Their mesial walls are however thicker than the 

 lateral walls. As these sacs expand they acquire, in tranverse 

 section, a more or less crescentic outline, their concave sides being 

 turned towards one another and enclosing the future oesophagus 

 (Fig. 58A and B, AntMeso). At Stage XIII the extreme mesial 

 edges of these coelomic sacs, corresponding to the dorsal points of 



