102 THE EMBRYOLOGY OF THE HONEY BEE 



by pale crescentic areas. Extending the entire length of the germ 

 band, from the stomodaeal invagination to the caudal end, is a 

 wide shallow groove, the neural groove. This is bounded laterally 

 by a pair of low ridges, the neural ridges. From the ectoderm 

 included in the neural groove and the neural ridges the ventral 

 nerve cord is formed. 



The invaginations forming the silk glands have now lengthened 

 out to tubular sacs extending caudad and slightly laterad, but as 

 yet not reaching the posterior border of the first trunk segment. 



The definitive number of tracheal invaginations on the trunk, 

 ten pairs in all, are now present, and appear as narrow slit-like 

 openings. 



The stomodaeal depression has deepened, becoming funnel- 

 form. 



The invagination forming the anus, the proctodaeum, and those 

 forming the Malpighian tubules, also appear at this stage, but 

 are not apparent from the ventral side. Their formation will be 

 more fully described in the sections devoted to the alimentary 

 canal. 



Stage X. Estimated at 54-56 hours (Figs. X and Xa). At 

 this stage several well marked changes in the general appearance 

 of the embryo are noticeable. The cerebral lobes do not now 

 plainly show their subdivision into protocerebral and deutocere- 

 bral lobes, they form instead conspicuous hemispherical swellings, 

 one on each side of the head, which on the dorsal side are marked 

 off from the trunk by a deep constriction. The labrum (Lm) has 

 become a conspicuous conical process projecting out from be- 

 tween the cerebral lobes parallel to the long axis of the embryo 

 and is somewhat flattened dorsoventrally ; its tip is seen to be 

 plainly bilobed. 



The stomodaeal invagination (Sto) has lengthened to a short 

 tube, and its connection with the mid-intestine, whose outlines 

 are now plainly visible, is much more apparent. The tritocerebral 

 lobes are scarcely visible and are in fact in process of flattening 

 out and disappearing. The antennal rudiments and mouth parts 

 have changed but little, except that the latter have lengthened a 

 little in a dorsal-ventral direction and are beginning to take on 

 their characteristic forms, the mandibles being long papillate, 

 while the two pairs of maxillae are shorter and more blunt, some- 



