THE EMBRYOLOGY OF THE HONEY BEE 107 



An-' 



Fig. 36. Diagram of a generalized insect embryo, showing the segmenta- 

 tion of the head, thorasic, and abdominal regions, and the segmental 

 appendages. From Snodgrass (1910). 



in the insect embryo, as distinguished from the secondary or 

 definitive head and trunk divisions of the imago. The primary 

 head division comprises those segments whose ganglia unite to 

 form the supraoesophageal ganglion or brain. The number of 

 segments entering into this division has been variously estimated ; 

 Janet (1899), basing his conclusions on a study of the structure 

 of the head of an adult wasp, Vespa, enumerates seven, while 

 Carriere finds four in Chalicodoma, but it is probably safe to say 

 that the majority of investigators follow Viallanes (1887), Patten 

 (1889), and Wheeler (1893) in recognizing but three segments. 

 These are: (1) the protocerebral, (2) the deutocerebral, and 

 (3) the tritocerebral. The first of these is without true append- 

 ages ; the second bears the antennae, the third bears in some of the 

 more primitive insects vestigal appendages probably correspond- 

 ing to the second antennae of the Crustacea, as the researches of 



