248 THE EMBRYOLOGY OF THE HONEY BEE 



Petrunkewitsch (1902) gives the following table for drone 

 (male) eggs: 



Age in hours Stage of development 



3-4 first cleavage spindle. 



4-7 cleavage. 



7-9 movement of the cleavage nuclei towards 



the periphery. 



9-20 formation of the blastoderm. 



20-25 blastoderm. 



25-36 gastrulation. 



36-38 end of gastrulation ; rudiments of the 



mesodermal tubes formed. 



According to these data it appears that the development of the 

 drone egg is more rapid than that of the worker (female) egg, 

 since "gastrulation," that is, the formation of the mesoderm and 

 the mesenteron rudiments, commences at least five hours earlier. 

 Unfortunately the time required for total development is not 

 known. 



Among other insects, the only data which are sufficiently com- 

 plete to be of value for comparison are those of Heider (1889) 

 for Hydrophilus. These are extremely full and explicit, and 

 include all of the more important phases of development of the 

 insect. They are arranged in the form of a table which covers 

 two and a half folio pages and therefore far too elaborate to be 

 reproduced here. It will nevertheless be profitable to compare 

 Hydrophilus and the honey bee, using for this purpose certain 

 more or less arbitrary periods into which the development may 

 conveniently be divided. 



Kowalevski (1871) distinguishes three periods in the develop- 

 ment of Hydrophilus. They are as follows: The first extends 

 to the complete formation of the germ band and of the 

 embryonic envelopes. The second includes the formation of 

 appendages and the origin of the glandular layer of the intestine 

 ("Darmdriisenblatt"), up to the formation of the dorsal plate and 

 the rupture of the embryonic envelopes. The third includes the 

 complete differentiation of the embryo and the dorsal wall of the 

 mid-intestine. Heider (1889) interprets these periods as follows: 



