BRAINS OF THREE GENERA OF ANTS 537 



ward or outward, but the fact that the diameter of the root is 

 slightly greater at its anterior end seems to indicate that some 

 fibers must enter as well as leave the stalk. Anterior to figure 

 25 the two bundles of transverse fibers fuse into one (fig. 10). 

 The anterior root ends on the antero-dorsal surface of the proto- 

 cerebral core in a loose network of fibers. 



The posterior roots of the mushroom bodies have already been 

 described under the heading "Tubercles of the central body." 

 To restate briefly: The distal end of each stalk, the previously so- 

 called 'inner' root, divides beneath the central body into two 

 bundles, a dorsal and a ventral, derived evidently from the fibers 

 from the inner and outer lobes; the two dorsal bundles pass into 

 the central body as the central body roots of the mushroom bodies, 

 the two ventral bundles, or the posterior roots of the mushroom 

 bodies, continue backward and enter the dorsal surface of the 

 hindermost part of the protocerebral lobes, in the region where 

 the protocerebral lobes are connected with the subesophageal 

 ganglion. 



b. The nerve cells of the mushroom bodies 



The cells of the mushroom bodies as seen in frontal sections 

 (figs. 32-34) are distributed into groups or zones which are usually 

 separated from one another by narrow spaces, so that the outlines 

 of the groups may be distinguished even with a low power. The 

 study of these cell groups with an oil immersion lens reveals 

 slight but constant differences in the size and arrangement of 

 the cells (fig. 29). The groups are the same in both outer and 

 inner lobes. Four kinds of cells are distinguishable; in an entire 

 lobe these are arranged in four zones encircling the calyx, but 

 in sections they appear as seven cell groups, described here for 

 the first time. In figure 29, Group I, is the oval mass of large 

 cells in the center of the calyx or cup; Groups II, L, II, r., are the 

 broad fan-shaped masses of cells occupying most of the dorsal 

 surface of the lobe; Groups III, L, III, r., are broad aggrega- 

 tions of cells forming the sides of the cup; Groups IV, L, IV, r., are 

 small masses of cells at the base of the cup. Only the nuclei of 

 these cells are drawn in figure 29, but cell bodies are shown in 



