552 CAROLINE BURLING THOMPSON 



The male has the smallest head and brain, with usually the 

 largest eyes. The optic lobes are very large and curve downward. 

 The mushroom bodies, though actually smaller than in the other 

 castes, are relatively large in proportion to the size of the brain. 

 The same is true of the antennary lobes. 



The queen of Lasius niger has a more generalized and superior 

 type of brain than the queens of Formica and Camponotus, which 

 show evidence of reduction or degeneration, especially in the mush- 

 room bodies. 



The queen brain in its typical generalized condition, as for 

 example in Lasius niger, is superior to and more highly developed 

 in all respects than that of the worker; therefore, the queen brain 

 represents the primitive generalized type from which the worker 

 has been derived. 



DISCUSSION OF RESULTS 



The great complexity and the high degree of differentiation re- 

 vealed by a close study of the mushroom bodies are additional 

 evidence in favor of the view held by many investigators of the 

 ant brain — notably Dujardin, Ley dig, Forel, Viallanes — that 

 these bodies are the chief motor and psychic centers of the brain. 

 The differentiation of the mushroom body cells into groups, the 

 number, constancy, and definite arrangement of the fiber tracts 

 arising from these cells or ending about them, and the connection 

 of the mushroom bodies with the other parts of the brain are 

 points of structure that indicate their importance. If the Cajal 

 method, tried so successfully by Jonescu for the honey bee, can 

 be made to succeed with ants, as I hope later to do, I am con- 

 vinced that even more complex arrangements of fiber tracts will 

 be revealed. 



The discovery of the connection of the posterior roots of the 

 mushroom bodies with the protocerebral lobes should fill a large 

 gap in our knowledge of these bodies. If the mushroom bodies 

 are the important motor and psychic centers of the brain it 

 seems strange that their connections with other parts of the 

 brain should be as slight as has been heretofore described. The 

 previously described connections of the mushroom bodies with 



