BRAINS OF THREE GENERA OF ANTS 523 



equal, in size to those of the worker, Lasius, or smaller than in 

 the worker, Camponotus, Formica. Compared with the male, 

 the queen's compound eyes are usually slightly smaller, the ocelli, 

 either larger, Camponotus, or smaller, Formica, Lasius. 



2. The worker brain 



a. Camponotus worker: figure 2. The brain occupies about 

 two- thirds of the width of the head. It is nearer the apex of 

 the head than in the queen but farther away than in the male. 

 The distinguishing characters of this brain are its highly developed 

 mushroom bodies, mh., and its greatly reduced optic lobes, o.l. 

 The mushroom bodies make two huge swellings on the dorsal 

 surface, almost touching one another in the median line and 

 extending far out in the lateral direction. The cups are more 

 deeply lobed than in any other caste and the large swollen ends 

 of the crescents make these bodies very prominent. The optic 

 lobes are reduced in both directions. This reduction is evidently 

 correlated with the reduced size of the compound eyes. Ocelli 

 are entirely absent in this worker. 



6. Formica worker: figure 5. The brain occupies more than 

 two-thirds of the width of the head and lies at about the same dis- 

 tance from the apex as in the other two castes of this genus. 

 Although the heads of the worker and queen are about similar 

 in size the worker brain is actually larger than that of the queen. 

 Both mushroom bodies, m.h., and optic lobes, o.l., are much larger 

 and the optic lobes are thicker and curve a little downward 

 toward the large well developed compound eyes, as in a male 

 brain. The mushroom bodies project prominently on the dorsal 

 surface, but do not approach each other as much as in the Cam- 

 ponotus worker. The ocelli are reduced in size. 



c. Lasius worker: figure 8. The brain of this form occupies 

 nearly the whole width of the head. The reduced size of the 

 optic lobes, o.l., and the large well developed mushroom bodies, 

 m.h., are characteristic. As stated above, the mushroom bodies 

 are equal to or slightly larger than those of the queen. Like 

 the worker of Camponotus, the reduction of the optic lobes is 



