52 THE EMBRYOLOGY OF THE HONEY BEE 



The writer has so far not studied the drone egg, and can there- 

 fore not make any statements in regard to it ; a rolling up of the 

 edges of the middle plate was however not observed in any of the 

 preparations of the worker eggs. 



Coincident with the process of mesoderm formation is another 

 phenomenon, that of segmentation or metamerism. This is ob- 

 servable as early as Stage V, and on surface view is evident in 

 the form of alternating transverse light and dark bands or zones 

 extending across the ventral plate and appearing first in its 

 anterior region just behind the anterior mesenteron rudiment. 



Three of these bands are to be seen in figure V. They make 

 their appearance in rapid succession from in front backwards 

 until at Stage VII they have reached the posterior region of 

 the egg, when at least fourteen of them can be counted. A 

 glance at the next stage, VIII, when the rudiments of the ap- 

 pendages and stigmata make their appearance, suffices to show 

 that the darker zones undoubtedly correspond to the definitive 

 segments of the embryo. Longitudinal sections of Stage VI 

 show that the alternating darker and lighter zones are only the 

 optical expression of alternating thinner and thicker zones in 

 both the middle and lateral plates ; in other words the segmen- 

 tation affects both the future mesoderm and ectoderm (Figs. 

 22 A and B, and 23 A and B). 



The segmentation of the middle plate is at best rather ill 

 defined, and most marked in the mid-line of those portions about 

 to be covered by the lateral plates (Fig. 22 A). The latter show 

 a segmentation corresponding to that of the middle plate and ex- 

 pressed in the same manner, namely by a wavy contour of their 

 inner boundaries when seen in longitudinal section (Fig. 22B). 

 In figure V, where three dark zones are faintly visible at the 

 anterior end of the middle plate, the free edges of the lateral 

 plates at their anterior ends are lobed or scalloped in such a 

 way as to suggest segmentation, the lobes of the two opposite 

 sides corresponding to one another and also to the dark zones 

 of the middle part. The same is true of the lateral plates near 

 their posterior ends at the following Stage, VI. Segmentation 

 (metamerism) thus appears simultaneously in the lateral plates 

 before their union, in the flask stage, and is accompanied by a 

 corresponding segmentation of the middle plate. It begins first 



