THE EMBRYOLOGY OF THE HONEY BEE 221 



The hind-intestine is a short tube, of about the same diameter 

 as the oesophagus, bent in a gentle sigmoid curve, and tra- 

 verses the three terminal trunk segments (Fig. XV, Hint). Its 

 blind anterior end rests against the posterior end of the mid- 

 intestine ; its posterior end opens to the exterior at the posterior 

 end of the trunk. Its structure is much the same as that of the 

 oesophagus, except that its lumen is circular and relatively 

 smaller. 



The Malpighian tubules, four in number, open into the anterior 

 blind end of the hind intestine (Fig. XV, Mai). From here they 

 extend cephalad in a winding course to about the sixth trunk 

 segment. Their diameter is slight, somewhat less than that of 

 the lateral tracheal trunks, and is uniform throughout their length 

 (Fig. 75, Mai). Their lumen is relatively small and circular in 

 section. 



The mid-intestine or mesenteron is derived exclusively from the 

 anterior and posterior mesenteron rudiments. At Stage VII 

 (Figs. 26B and 29, AMR) the anterior mesenteron rudiment is a 

 thick convex disk of cells resting on the ventral side of the yolk, 

 at the cephalic end of the egg. This disk is covered by the ecto- 

 derm with the exception of a small area at its posterior margin, 

 where the cells of the disk extend through a gap in the ectoderm 

 to the external surface (Fig. 26B). During the interval between 

 Stages VII and VIII the germ band rapidly increases in length, 

 the effect of this being to cause the cephalic end of the germ band 

 to travel around the cephalic pole of the egg, carrying with it the 

 anterior mesenteron rudiment, which assumes a position on the 

 cephalo-dorsal face of the yolk. In this position the morpho- 

 logical posterior margin of the rudiment, where its cells reach the 

 external surface, lies approximately at the cephalic pole of the 

 egg. This rudiment, as a whole, has at first the form of a thick 

 cap, but by the time Stage VIII is reached, it has become elongated 

 in a longitudinal direction. Its form may then be compared with 

 that of a spoon or scoop (Fig. 87A). The part corresponding to 

 the handle is situated at the cephalic pole of the egg, where the 

 stomodaeum (Stom) has already put in its appearance, and here 

 it penetrates the ectoderm to the exterior, forming the bottom of 

 the stomodaeal depression, while the remainder, corresponding to 



