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C. JUDSON HERRICK 



ganoid fishes, a group which, though retained in popular usage, 

 is now without scientific status. Paleontologists follow the 

 branch of 'lobe-finned ganoids' containing Polypterus back to 

 a common origin with the lungfishes and far removed from the 

 forms ancestral to the other groups of recent fishes (Osborn, 

 '17, fig. 50, p. 168). 



In Polypterus the olfactory bulbs are fully evaginated and the 

 primitive endbrain is greatly elongated. The side walls are 



OLfACTORY BUL8 



D VENTRICLE 



Fig. 11 A transverse section through the primitive endbrain of Polypterus 

 bichir between the terminal plate and the betweenbrain. The thin but massive 

 side walls are everted and the wide common ventricle is roofed by membrane only. 

 The median longitudinal fold of the roof accentuates the illusory appearance of 

 distinct cerebral hemispheres similar to those of Protopterus (fig. 13), but there 

 is no real resemblance. Redrawn after Waldschmidt ('87, fig. 4). 



Fig. 12 Diagrammatic longitudinal section of the forebrain of Protopterus, 

 illustrating the fully evaginated cerebral hemispheres. The figure is based on 

 the drawings of Burckhardt ('92) and is purely schematic. 



massive and the roof membranous, as in the sturgeon (figs. 4, 

 5) , but the massive walls are thin and strongly everted, as shown 

 in figure 11. When the membranous roof is stripped off, the 

 appearance of this brain seen from the dorsal side presents a 

 superficial resemblance to that of Protopterus (figs. 12, 13), 

 but the resemblance is wholly illusory, for no part of the end- 

 brain of Polypterus behind the olfactory bulbs is evaginated and 

 the elongation of the so-called hemispheres is altogether behind 

 the terminal plate. 



