666 BASHFOKD DEAN, 



forebraiü, for precisely similar characters have been shown to occur 

 in Ämia. It is further evident that the brain of the bony fish is so 

 closely Amioid that it may reasonably be looked upon as but a high 

 degree of specialization of this neo-gauoidean type. The development 

 of the brain of the Teleost is fully in keeping with the precocious 

 growth rate of its other structures : by the time of hatching the brain, 

 Fig. R, has assumed far more nearly its adult characters than has 

 that of a month old Ämia, Fig. Q. 



The subject of the roof of the forebrain deserves a final word, 

 especially in view of the unorthodox position of Beard ^). For, ac- 

 cording to this writer, the pallium of lamprey and Teleostome was 

 the homologue of the choroidal plexus of shark, lung-fish and am- 

 phibian ; and it was, accordingly, taken as a most important character 

 to separate two phyla of fishes. That this position is untenable is 

 now evident from the studies of Burckhardt on the forebrain of 

 fishes, especially as to the increase in its ependymal region, in which 

 are traced well raarked transitions from Selachian to Teleostean conditions. 

 The results of Burckhardt ^) are further confirmed by the study of the 

 mode of development of the forebrain among the three types of 

 Ganoids; for in these, as in a graded series, it may be shown that 

 the ependymal region increases in size as the more modern type, 

 Ämia, is attained. 



Neuromeres. 



The recent memoir of Locy ^) has directed renewed attention to 

 this subject. In Ämia the discussion of neuromeres belongs more 

 strictly to the period of later embryonic development and will not 

 therefore be included in the present paper. Note should be made, 

 however, of the very prominent neuromeres which appear in the floor 

 of the bind brain, beginning imraediately on either side of the sagittal 

 plane, in the stages figured in PI. 9, Figs. 1—7. These may be seen 

 in the section of Fig. N, in which the bind brain has been cut in a 

 favorable plane : five neuromeres are shown, the niiddle one the most 

 prominent, the fore- and hindmost ones fading away into the region 

 of the plica ventralis and cord respectively. Similar conditions, but 



1) On the interrelationships of the Ichthyopsida, in: Ariat. Anz., 

 V. 5, 1890, p. 146—159. 



2) in: Anat. Anz., V. 9, No. 12, p. 375—382. 



3) in: J. Morph., V. 11, 1895, No. 3, p. 497—594. 



