BRAINS OF THREE GENERAOF ANTS 525 



2. THE PROTOCEREBRAL LOBES 



The protocerebral lobes, '^les lobes protocerebraux" of Vial- 

 lanes ('86), consist of a central core of fibrous reticular substance, 

 surrounded by an outer zone of nerve cells (figs. 1-9). The fibrous 

 substance is composed of: (1) nonmedullated nerve fibers, axons, 

 usually possessing a neurilemma or nucleated sheath, (2) the 

 branching dendrites of the nerve cells, and (3) of supporting cells. 

 The nerve cells that immediately surround the fibrous core of 

 the protocerebral lobes, usually in a single layer, are very small 

 with very little cytoplasm. The outermost cells are large, some 

 very large, with more abundant cytoplasm and large round nuclei. 

 These cells are usually arranged in bunches or masses several 

 cells deep, with their axons running inward to the fibrous core. 

 The median dorsal region, both in front of and beneath the 

 mushroom bodies, called by Haller ''the pars intercerebralis," or 

 intercerebral region, is characterized by a looser, more open 

 appearance and by the presence of numerous very large ganglion 

 cells. One of these cells is shown in figure 31. These are, how- 

 ever, not confined to the dorsal region but are found also on the 

 ventral surface of the brain. Jonescu ('09, p. 141) has noted 

 the same facts in the honey bee : 



Die Protocerebralloben sind an alien Seiten von einer diinnen Schicht 

 kleiner Assoeiationszellen umgeben. Ausserhalb dieser Schicht findet man 

 eine Schicht grosser Ganglienzellen (Verbindungselemente) .... 

 Diese Schicht besitzt auffallig grosse Zellen. Solche Zellen sind aber 

 nicht nur an der dorsalen Seite der Protocerebralloben lokalisiert, 

 sondern ich habe sie auch auf der Ventralseite der Loben gefunden. 



To understand the relation of the protocerebral lobes to the 

 other parts of the brain, a series of frontal sections taken at 

 varying distances from one another from the brain of the Lasius 

 queen, beginning at the anterior end and going backward are 

 shown in figures 10 to 16. It wdll be noted in figure 10 that the 

 fibrous core of the protocerebral lobes, p. I., is one single solid 

 mass, penetrated by the anterior roots of the mushroom bodies, 

 a.r., and on the ventral surface extending into two tiny fibrous 

 masses, the optic bodies, o.h., 'tubercules optiques,' Viallanes. 



