H E R R I c K , Morphology of N'crvons System. 1 6 1 



easily recognized by tlie epithelial covering of the axial lobe 

 where it is present. 



The conversion of the free portion of the mantle to a 

 function less membrane is carried to its extreme in fishes, but 

 birds furnish many resemblances. 



The cerebrum is more highly developed in Lepidosteus. 

 Cephalad, it projects beyond the olfactory, and appears in 

 transection as two independent bodies dorsad to the olfactory 

 lobes. Plate XIII, Fig. i, illustrates a section through the 

 olfactory and extreme cephalic part of the lateral ventricle, 

 which is bounded only by the pallium. The relations are 

 essentially the same in all ganoids. Fig. 3, which passes 

 through the corpus callosum, shows the relation between the 

 olfactory aqueducts and lateral ventricle. The real homo- 

 logues of the foramina of Monro are considerable slits. In 

 the sturgeon, as may be gathered from Plate XI, Fig. 2, the 

 relations are similar, but the partial eversion of the hemi- 

 spheres laterally brings the opening of the aqueduct of the 

 olfactory lobes farther laterad. 



In the figure, because of some distortion in the section, 

 the median walls of the ventricles have been rendered 

 asymmetrical, and the openings of the foramina of Monro 

 appear too large. 



In Fig. 3, of the same plate, the median walls are 

 occupied by the plexus, which is shaded dark. 



The middle portion of the hemispheres are somewhat 

 quadrangular in transection (Plate XIII, Fig. 3). Cephalad, 

 the dorsal portion projects laterally considerably, while 

 further caudad the lateral aspects are nearly perpendicular. 

 The two hemispheres become separate at the chiasm, the 

 connection being formed by a portion of the velum, united 

 with the cephalo-lateral aspects of the habena;. 



Respecting the dorsal sac, Lepidosteus affords much clearer 

 information than the sturgeon, and renders necessary a con- 

 siderable change in the interpretation of this structure, 

 offered by Goronowitsch. Morphologically it is a dorsal 



