THE EMBRYOLOGY OF THE HONEY BEE 157 



Wheeler, Heymons and others, especially with regard to the 

 division of the insect brain into three segments or neuromeres. 

 Second, with regard to details, the brain of the bee shows several 

 points of difference when compared with the few accounts avail- 

 able. These accounts relate principally to the development of the 

 brain in Orthoptera, and the nearly allied Dermaptera, as exem- 

 plified by Forficula. In fact since the publication, in 1895, of 

 Heymons' monograph, there has appeared no detailed account of 

 the embryonic development of the insect brain. Even Carriere 

 and Burger (1897), in their otherwise quite complete account of 

 the development of the mason bee, give a disappointingly brief 

 account of the brain, concluding with the statement that "An 

 extended account of the development of the brain may be omitted, 

 since it would only serve to confirm the more recent investigations 

 on this subject." 



The points in regard to which the development of the brain of 

 the bee differs from the Orthoptera and Dermaptera may be 

 summed up as follows : 



(1) The brain is flexed around the cephalic pole of the egg in 

 such a way that the morphological anterior ends of the proto- 

 cerebral lobes are directed toward the caudad pole of the egg. 



(2) The cells of the second generation from the neuroblasts, 

 instead of the first, form the definitive nerve cells. This is the 

 same as in the ventral cord. 



(3) The three subdivisions of the protocerebrum are not at 

 first plainly marked off from one another and are never separated 

 by hypodermal ingrowths. 



(4) The optic lobes are formed, apparently independent of the 

 agency of neuroblasts, by a deep invagination of the neurogenic 

 ectoderm, which has no counterpart in the Dermaptera or Orthop- 

 tera, but seems to correspond more or less closely with an invagin- 

 ation of the optic lobe described by Patten (1889) in Acilius and 

 Heider (1889) in Hydrophilus. Patten (1887) has also described 

 an invagination concerned in the formation of the optic lobe in 

 Vespa which seems to be similar to that in the honey bee. 



C. The Stomatogastric System 

 The stomatogastric system, as in other insects is formed from 

 the dorsal wall of the stomadaeal invagination. The rudiments 



