Kingsbury, Brain of Necturus. 159 



only be directly changed into those of higher forms, by the mi- 

 gration of the bundle in question across the portas. 



It is to be regretted that no satisfactory solution of the dif- 

 ficulties involved can be offered here. It is believed as stated 

 by Herrick that the "whole question as to the relation of the 

 qalloso-fornix structures requires spfcial consideration on the 

 widest possible comparative grounds." A callosum at least 

 seems to be entirely absent. I fail utterly to find any trace of 

 a commissure in the terma cephalad of the porta where Herrick 

 has figured it in Nectiinis. Judging from the figures and state- 

 ments of Edinger, Herrick and Meyer, what has been called 

 the hippocampal commissure in Reptiles lies caudad of the por- 

 tas in the roof ; hence the readiness with which Herrick consid- 

 ered the commissure in Ncctiiriis a hippocampal commissure, 

 since he regarded it as dorsal. A comparison with the cerebral 

 commissures of the reptilian brain has not been made in this in- 

 vestigation and an expression of opinion cannot be given as to 

 the comparability of the relations in Amphibia and reptiles. It 

 is believed, however, that this commissure will prove, in part at 

 least, a hippocampal commissure. 



Whatever may be the result of exact comparison with the 

 cerebral commissures of Reptiles, it is felt that a representative 

 of this commissure should be looked for in other Ichihjopsida, 

 which have other characters of the brain in common. It is 

 hardly necessary to mention the importance of a knowledge of 

 the relations that the cerebral commissures have in the three 

 Dipnoans. Burckhardt (9) has found it in the brain of Protop- 

 teriis and calls it a callosum, but he says nothing of the distri- 

 bution of the fibers, nor do his figures afford a solution. Ccr- 

 atodiis and Lcpidosircn yet await investigation. The fact that in 

 Petromyzon a cerebral commissure has been recognized in ad- 

 dition to the precommissure, lends the hope that the conditions 

 there may be found to compare closely with those in urodeles, 

 the general resemblance between whose brains has been noted 

 by Wilder i^T^)- Mrs. Gage has contrasted transections 

 through the cerebral commissures in Dieviyctyliis and Ainia, and 

 has suggested that the (ventrally) recurved portion of the cere- 



