Herrick, Morphology of Brain of Bony Fishes. 71 



Fig. 2. Section of a similar brain longitudinally of the tectum, 

 especially designed to show the termination of optic nerve fibres in the 

 cells whose apex processes divide in the ectal reticulum. 



Fig. 3. A small portion of a similar section to demonstrate the con- 

 nection of the ganglion cells with the descending tract. 



Fig. 4. A portion of the nidulus niger in the drum, illustrating the 

 form of the switch ceils in the dorsal part of the hypoaria. 



Fig. 5. Similar region of perpendicular section to demonstrate three- 

 fold connection, i. e., with region of ventral peduncles, tract to cerebellum, 

 and dorsal peduncles. 



Fig. 6. Marginal cells of hypoaria in the drum. 



Fig. -. Cells from the ventral part of hypoaria in nine days old 

 Trutta fario. The ventral peduncle fibres a-re fit the right. 



Fig. 8. Cells of the marginal part of hypoaria in the drum, showing 

 connection with ventral peduncles and probable secondary branch to anasta- 

 niose with cerebellar and dorsal peduncle. ' 



Fig. 9. Region of nidulus ruber (catfish ?) 



Fig. 10. Portion of the nidulus ruber [Lucioperca .) 



Fig. II. Portion of nidulus ruber (/('■«//i?/a'()«^/«.f.) 



PLATE X. 



This plate is intended to illustrate the extreme simplicity of the 

 histological elements in the Urodela. The figures are all derived from a 

 series of horizontal sections of Menopoma alleghenensis, stained with hsema- 

 toxylin. The stain is a nucleary selective agent in this case but with suf- 

 ficient care the cell body and processes can be made out with considerable 

 detail. Figs. 1-4 are horizontal sections through the cerebrum and mes- 

 encephalon at different levels. The letters in Fig. 2 refer to areas shown 

 below on an enlarged scale. 



Fig. 1^. Portion of optic lobes and thalamus with postcommissura 

 enlarged from Fig. 2. The right side of the figure indicates a few isolated 

 cells and fibres in a semi-diagramatic way for reference, the left side is 

 drawn with a camera although the outlines of the cells are not given with 

 precision. H. portion of the left hemisphere, i, habena and portion of 

 the tienia, ^, tract of superior commissure, c, centre of origin of Meynert's 

 bundle ? e, posterior commissure, a, large cells supposed to be homologous 

 with the mesencephalic nidulus of the 5th nerve, b, tract,/, optic tract. 



