Fish, Brain of the Fur Seal. 87 



changes effected in passing from simple to complex conditions. 



In the general form of the brains that of the sea lion 

 seemed to bear closer resemblance to that of the bear than either 

 Callorhinus or PJioca — the latter the least of all. The elongated 

 and narrow frontal portion of the brain as seen in the bear is 

 represented in Phoca by a foreshortened and broadened region, 

 less marked in Callorhinus and still less in Zalophus. 



The development of the olfactory lobes is also interesting. 

 They attain their highest growth in the bear, next in Zalophus, 

 then Callorhinus and least in Phoca. 



The triangular area on each hemicerebrum located between 

 the cruciate and precruciate fissures and the intercerebral cleft, 

 designated by Mivart as the ursine lozenge and believed by him 

 to be of considerable importance in indicating a phylogentic 

 relationship between the Pinnipedia and the ursine group of 

 carnivora, was developed equally well in Zalophus and Callor- 

 hinus. In Phoca it was not observable, althougn Turner states 

 that in this form it is present but rudimentary and concealed in 

 the mesal fissure of the cerebrum. 



The length of the lateral fissure in Callorhinus is somewhat 

 unexpected and in relation resembles a continuous lateral and 

 ectolateral of the bear. In the sea lion and Phoca the lateral is 

 a relatively short fissure. In all but the bear there is an inde- 

 pendent ectolateral fissure but it is not so satisfactorily devel- 

 oped in Phoca. 



The postrhinal fissure shows an interesting variation in the 

 different forms. In CallorJiinus and Zalophus it has no connec- 

 tion with the rhinal or Sylvian, but it is a direct continuation of 

 the subfissure — postica. In Ursiis the subfissure may occasion- 

 ally reach it but as a rule it is distinct and the postrhinal con- 

 tinues as an elongation of the rhinal. In Phoca the separation 

 of the subfissure and the postrhinal is still more marked, so that 

 the rhinal and the postrhinal are practically different parts of 

 one 'and the same fissure, differentiated from each other by the 

 presence of the Sylvian. 



The presupersylvian fissure is directly continuous with the 

 supersylvian in Ursus, it is likewise continuous in Zalophus and 



