BRAINS OF THREE GENERA OF ANTS 543 



to cells in the mandibular lobe. There is an opportunity for 

 an exchange of fibers between b and the mushroom body, since 

 the fibers of each touch one another without any intervening 

 sheath, and in places fibers may be seen passing out of the cup 

 into b. 



Tract c consists of fibers arising in Group III, r. of the inner 

 lobe. The fibers run downward and outward, crossing in front 

 of the stalk of the outer lobe, dorsal to the lateral part of b, 

 and entering the protocerebral tissue just lateral to and in 

 close contact with the fibers of b. The central part of c is pres- 

 ent in three sections. This is a very noticeable tract on account 

 of its direction and its size. It is present in all three queens and 

 in the male of Camponotus. 



Tract d, present only in two sections, is a narrow inconspicuous 

 bundle of fibers arising from Group IV, I, of the inner lobe and 

 ending in the inner protocerebral tissue. Its fibers sometimes 

 pass through the anterior protecerebral commissure. Z) is a 

 tract that has been found only in the queen caste. 



Tract e, present in two sections, originates in Group III, I, 

 of the inner lobe. Its fibers occupy most of the inner part of 

 the calyx, then run downward and inward, and leaving the stalk 

 of the inner lobe, terminate in the protocerebral tissue posterior 

 to and on the median side of the terminal fibers of d. E is found 

 in all castes of Camponotus, but only in the workers and males 

 of Formica and Lasius. 



Tract/ is present in two sections and is a narrow band of fibers 

 connecting the outer and inner lobes. The fibers seem to arise 

 from the Groups IV of both lobes, but it is impossible to state 

 whether the fibers run in both directions or only in one. 



Tract I, a curved band of fibers lying beneath / and separated 

 from it by a space filled with supporting cells, lies two sections pos- 

 terior to/ and is quite distinct from it in the queen of Camponotus. 

 In all the other forms / and I are united into either a simple or 

 a double commissure, and are present therefore in the same sec- 

 tions. L, as seen in the Camponotus queen, is a rather stout 

 band of fibers running between the outer and inner lobes, with 

 its central part at a more ventral level than /, but arising at a 



