CONTRIBUTIONS TO THE COMPARATIVE 



MORPHOLOGY OF THE CENTRAL 



NERVOUS SYSTEM. 



( Continued.) 



III.— TOPOGRAPHY AND HISTOLOGY OF THE BRAIN OF 

 CERTAIN GANOID FISHES.— Plates XI and XIII. 



It seems desirable for several reasons to introduce at this 

 point in the series a few data relating to the Ganoid brain. 

 The Ganoids form a natural point of departure for any 

 minute study of the brains of the lower fishes, and if the 

 peculiarities of structure which at first seem so irreconcilable 

 can be shown to present no morphological difficulties, one 

 may hope to be able to apply the homologies made out in 

 such a typical brain as that of a lizard to any vertebrate. As 

 a matter of fact, no better illustration of the value of morpho- 

 logical generalizations in the solution of special problems 

 need be sought than that afforded by the complete and satis- 

 factory solution of the puzzle so long unread in the case of 

 the brain of fishes. Thus the Ganoids are found to possess a 

 brain curiously modified, it is true, but one in which every 

 important organ of the reptilian brain may be satisfactorily 

 identified. The laws of development, read backward, enable 

 us to trace the connection very satisfactorily in most cases, 

 while the aberrant features are found to be modifications of 

 familiar organs rather than new structures. 



A brief outline is offered at this time relating to the 

 topography and a few points only in the histology of the 

 cephalic parts of the brain. Two types are used, and one or 



