256 THE EMBRYOLOGY OF THE HONEY BEE 



ilar but slighter fold is later formed at the caudal end of the egg. 

 The two folds meet and coalesce near the caudal pole. The am- 

 nion probably corresponds to the serosa of other pterygote insects. 



Twenty-one segments were found in the bee embryo, including 

 an anal segment or telson. Appendages were observed on the 

 antennal segment, the three gnathal segments, and the three tho- 

 racic segments. No abdominal appendages were found. The 

 antennal rudiments and those of the three thoracic legs became 

 reduced to hypodermal thickenings prior to hatching. The sup- 

 posed appendages of the premandibular segment are only exag- 

 gerated ganglionic swellings. No evidence of the presence in the 

 bee of a superlingual segment (Folsom) was found. As is 

 usual in insect embryos, the second maxillae fuse to form the 

 labrum. 



The rudiments of the nervous system take the form externally 

 of two longitudinal swellings of the ectoderm, the primitive swell- 

 ings, one on each side of and close to the ventral mid-line. At the 

 oral region these diverge, and in the cephalic region of the embryo 

 expand into the broad procephalic lobes. The primitive swellings, 

 including the procerebral lobes, are divided by slight interseg- 

 mental constrictions into twenty neuromeres corresponding to the 

 segments of the embryo. Two of these, formed from the 

 procerebral lobes, are preoral. The first, the protocerebrum, 

 corresponds to the primary head segment, the second, the deuto- 

 cerebrum, to the antennal segment. The two lobes constituting 

 the protocerebrum become rather obscurely subdivided into three 

 lobes, the most anterior of which become the optic lobes. During 

 the formation of the primitive swellings the germ band lengthens, 

 so that its cephalic end, including the procerebral lobes, becomes 

 curved around the cephalic pole of the egg. The protocerebral 

 lobes thus come to lie on the dorsal side of the egg with their 

 cephalic ends directed toward its caudal pole. Although the germ 

 band shortens somewhat at a later stage, the protocerebral lobes 

 always remain directed caudad, and not cephalad, as in more prim- 

 itive insects (e.g. Orthopetra). The third, neuromere, correspond- 

 ing to the premandibular or intercalary segment, is postoral, since 

 the commissure connecting its two lateral halves (ganglia) passes 

 below the stomadaeum. These three neuromeres become united 

 to form the supraoesophageal ganglion or brain. The neuromeres 



