144 THE EMBRYOLOGY OF THE HONEY BEE 



above the external surface of the egg as a more or less evident 

 swelling. Of these the protocerebral lobes (Figs. VIII, Villa, 

 iBr) are the largest. They are relatively flat with a rounded 

 external margin and have previously been described as resembling 

 a saddle in shape. The deutocerebral lobes (2Br) are more con- 

 vex, do not extend so far laterad, and are each tipped by a small 

 papilliform projection, the antennal rudiment (Ant). The trito- 

 cerebral lobes (sBr) are small hemispherical elevations situated 

 on a line with the posterior border of the stomodael depression 

 and somewhat farther apart than are the neural ridges to which 

 they are joined. They are in fact nothing more or less than the 

 much discussed "second antennae" of Biitschli and the "transitory 

 anterior appendage" of Grassi (see p. 109). A section transverse 

 to the long axis of the egg and passing through these three pairs 

 of lobes are shown in figure 52. 



On each side are seen the papilliform antennae (Ant), imme- 

 diately dorsad of which are the deutocerebral lobes (2Br). Above 

 these and divided from them by a slight depression are the anter- 

 ior ends of the protocerebral lobes (iBr) which extend almost 

 to the mid-dorsal line, being here joined together by a bridge of 

 small dermatoblastic cells (Hyp). Ventrad of the antennae are 

 the tritocerebral lobes (jBr), which are clearly seen to be essen- 

 tially similar to the remainder of the ganglionic swellings of the 

 neural ridges. Between these lobes, on the ventral side, is a pair 

 of high rounded elevations separated by a rather shallow median 

 depression. These elevations are merely the extreme anterior 

 ends of the neural ridges, which, at this and the stage next suc- 

 ceeding terminate anteriorly in a pair of rounded swellings situa- 

 ted just behind the mouth, and which are very evident in figures 

 IX and X. 



During Stage X the external elevations marking the two anter- 

 ior divisions of the brain become less evident, the outer surface 

 of the head becoming relatively smooth in contour. The swellings 

 forming the tritocerebrum tend to lose their prominence and at 

 Stage X (Fig. X) have almost disappeared. This flattening out 

 of the external evidences of the rudiments of the neuromeres of 

 the brain takes place at the same stage and corresponds with the 

 flattening out of the neural ridges in the trunk, the rudiments of 



