DETERMINATION OP AGE IN HONEY-BEES. 199 



having as a base a group of giant fibres. In each of the 

 dozen or so sections, 7 fi thick, passing thi-ough this region 

 there are generally four or five large cells — rather more in 

 very young brains. 



(2) Cells of the antennal lobes. Each of these lobes 

 consists of a convoluted spherical mass of fibres giving rise to 

 the antennal nerve and surrounded by nerve-cells. These 

 are the cells studied by Hodge (9, 10) and Smallwood and 

 Phillips (18). 



(3) Just anterior to the inner fibrillar body of the optic 

 lobe is a mass of cells, chiefly small ones, but with- a few giant 

 ones among thern. 



(4) Cells of the suboesophageal galnglion. The mass of 

 fibres forming the centre of the ganglion and giving rise to 

 the ventral nerve-cord is surrounded by a layer of cells which 

 is especially thick on its lower surface. It has been usual to 

 consider the suboesophageal ganglion as part of an insect's 

 brain (16, 8), since Faivre's physiological experiments (6) - 

 appeared to show that the power of co-ordinating the move- 

 ments of the body is there situated. This ganglion therefore 

 appears to correspond to the cerebellum of vertebrates. 



The.large cells, with nuclei 8-12 fx in diameter, from these 

 four regions in one and the same brain show great constancy 

 in appearance. They are also very similar to those from 

 other bees of the same age, but exhibit constant differences 

 from those of bees at other ages. 



On the whole it is most convenient to study the cells from 

 the fourth region, i.e. the suboesophageal ganglion. The large 

 cells here are very numerous, forming several layers below the 

 mass of fibres going to the ventral nerve-cord, and bounded 

 on each side by small groups of fibres, from which the 

 mandibular, maxillary and labial nerves arise (PI. 11, figs. 3 

 and 4). These layers of cells appear in about, ten serial 

 sections, and are therefore about 70 microns thick. In young- 

 bees they consist chiefly of large plump cells, only separated 

 from each other by narrow strands of connective tissue with 

 occasional connective-tissue cells (PI. 11, fig. 3). As the 



