Herrick, Morphology of Brain of Bony Fishes. 45 



or the planes of reference. The fibre tracts to be kept distinct 

 are, i. the optic fibres entering from the cephalo-mesal and 

 caudo-lateral aspects respectively. These tracts are part of the 

 same continuous sweep of fibres from the optic nerve, which 

 have been separated by the architectural necessities of the brain, 

 their internal course is morphologically identical. 2. The fibres 

 of the cephalic and caudal brachia which, after affecting cellular 

 connections at their exit from the tectum (?) connect with a 

 double commissural system (transverse and ventral commissures) 

 as above described. 3. The radiation to the lemniscus derived 

 from the ventral ganglionic series of the tectum and passing to 

 the lateral aspects of the medulla. 4. Associated with the lat- 

 ter the fibres of the middle peduncles of fhe cerebellum (decus- 

 satio tegmenti) and probably also fibres to the III, IV, and per- 

 haps the VI nerve niduli. There may also be among them 

 commissural fibres. 5. The sylvian commissure system whose 

 fibres pass in a more or less complicated course from one side to 

 the other, originating in the ectal reticulum of either side. 6. 

 A system of fibres belonging to the category of gelatinous tracts, 

 i. e. connective fibres springing from the epithelium of the ven- 

 tricular portion of the torus and passing to the ectal surface of 

 the tectum. This relation is especially well shown in Fig. 9, 

 Plate VII, and Fig. 8, Plate VIII. 



The connective frmnework of the tectum is constructed on the 

 same plan as that of the rest of the brain and consists of a con- 

 tinuous epithelium with the base of each cell upon the ventricle 

 and its summit at the periphery. The integrity of the series is 

 greatly disturbed by the development of neuroblasts and their 

 migration and the invasion of fibre tracts, as well as by the great 

 changes in position suffered as a consequence of the development 

 of the cerebellum and volvula. The primitive simplicity is re- 

 tained more perfectly in Amphibia {Menopoma, etc.) Fig. 12, 

 Plate X. To all appearances, the nucleus of the epithelium cell 

 divides without causing division of the cell, yet this is not cer- 

 tain. After passing the inner ganglion layer the walls collapse 

 and form a thread which may enclose one or more nuclei and 

 terminate at the periphery in a cell. Figs, i, 2, Plate IX. 

 These are conspicuous in the young, but practically shrivel up 

 with age. Between these cylindrical connective cells the neu- 



