CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
933 
certain, for even if they are natural and not artificial they might so collapse in the soft 
fresh state as to become obliterated. 
The Hypo aria. 
These bodies are not so well developed in the Mormyridce as in M. cephalus —they 
scarcely project at all below the ventral surface of the brain, and do not form separate 
lobes ; the ventricle is also very small; the trigonum fissum, however, is rather promi¬ 
nent, and forms a separate tubercle on the inferior surface. The hypophysis or 
pituitary body is attached to the apex of the trigonum, and the infundibulum passes 
through it. With regard to the minute structure of these parts it resembles that of 
the corresponding lobes in the M. cephalus in respect to the arrangement of the cells, 
which are dispersed separately throughout the neuroglia; but many of the cells them¬ 
selves differ in shape in being multipolar and in having as many as six processes, while 
some are pear-shaped. They usually measure about 0 - 0093 millim. by 0*007 millim. 
The nearly obliterated ventricle and the infundibulum are surrounded by a layer of 
small cells as in other Teleostei. These bodies may be considered to be in a rudi¬ 
mentary condition, and this is shown also by the absence of the nucleus rotundus and 
the transverse commissure connected with it. 
Tecta Lobi Optici. 
The position of these bodies in the Mormyriclce has become quite reversed. Instead 
of arching over the tori semicirculares on the dorsal side of the brain as in the ordi¬ 
nary Teleostei, they become relegated to the inferior surface and occupy a position 
below and to the outside of those bodies ; the roof in fact has been transferred to the 
foundation. 
The tecta appear to have attained this position in consequence of the enormous 
development of the wings alluded to in the first part of this paper. 
Accompanying this change of position there is a considerable degradation of struc¬ 
ture. The seven layers which are distinguishable in M. cephalus are here reduced 
to two or at the most three ; the ependyma has disappeared; there are only slight 
indications of radial st.riation. The outer layer in some places is separable into two 
subordinate divisions. The Mormyridce are not good subjects for deciding any histo¬ 
logical points in the structure of these lobes which as I have before remarked are 
decidedly undeveloped ; I was therefore not surprised to find that I am unable either 
to confirm or refute the statements of Bellonci" as to the presence of a minute net¬ 
work of fibrillse in the external layer of the tecta lobi optici, and I have not yet had 
* Ricerche intorno all’ intima tessitura del cervello dei Teleostei. Reale Aeeademia dei Lincei, Anno 
cclxxvi., 1878 and 1879. Also by the same author, tX den Ursprung des Nervus Opticus. Zeitschr. f. 
wiss. Zoologie, Bd. xxxv., 1880. 
