BRAINS OF THREE GENERA OF ANTS 551 



2. The dorsal protocerebral commissures 



The dorsal surfaces of the lateral parts of the protocerebral 

 lobes are connected by two bands of fibers termed respectively 

 in this paper, the anterior dorsal, and the posterior dorsal commis- 

 sure. The first of these is probably of compound nature. Both 

 commissures may serve as paths for the ocellar nerve fibers. 



S. The ocellar lobes and nerves 



The ocellar nerves enter the brain farther forward in the queen 

 than in the worker or male. The nerve from the anterior oeellus 

 divides into two, those from the posterior ocelli remain single; 

 within the brain these four branches enlarge to form the four 

 ocellar lobes which usually remain separate, but sometimes fuse 

 into two masses. The fibers from the ocellar lobes pass down 

 into the protocerebral lobes by different routes in the different 

 castes and genera. 



There is no connection between the ocellar nerve fibers and 

 the so-called ''ocellar glomeruli," which are really the posterior 

 roots of the mushroom bodies. 



4. The central body 



The central body consists chiefly of fibrous tissue. It is 

 connected by fibers with the protocerebral lobes and with the 

 mushroom body stalks. 



II. COMPARISON OF THE CASTES 



In the three genera under discussion the queen has the largest 

 head and brain. The brain appears laterally extended on ac- 

 count of the large laterally placed optic lobes. The mushroom 

 bodies are either equal to those of the worker, Lasius, or are 

 smaller than those of the worker, Camponotus, Formica. The 

 antennary lobes are larger than in the worker, Camponotus, 

 Lasius, or smaller, Formica. 



The worker brain has usually greatly reduced optic lobes and 

 eyes. In size the mushroom bodies exceed or equal those of the 

 queen. 



