106 GEORGE W. BARTELMEZ 
drite. It never reaches the lateral dendrite, which seems to be 
connected only with VIIIth root fibers. 
The axone cap is as striking and characteristic of Mauthner’s 
cell as are its great size and remarkable connections. This study 
was undertaken primarily to analyze the cap, a point which was 
essential to a full understanding of the central connections of the 
VIIIth nerve. Although it is improbable that I have made out 
all of its component parts, its essential nature at least is clear. 
It is, in fact, a peculiar synapse such as has not been found, so 
far as I know, in any other nerve cell. It is made up of at least 
three kinds of fibers, two of them nervous, the other supporting. 
These are: (A) collaterals from various neighboring fibers; (B) 
minute dendrites from the underlying ale of the cell body; 
(C) supporting elements. 
A. The collaterals ending in the axone cap stand out most 
clearly in Cajal preparations and are clearer in the older larvae 
than in the younger. Since Beccari (’07) worked mainly on 
young larvae, this accounts doubtless for his uncertainty concern- 
‘ing the nature of the axone cap in Salmo, where in reality it is 
essentially the same as in Ameiurus described below. The felt- 
work of collaterals is best shown in figure 10, in which the detail 
of the cap was drawn from a single 8 u» section. Eyen though 
the cell body had shrunken away from the cap, the relations of 
the fibers are perfectly clear. The figure shows three kinds of 
fibers giving off collaterals. First, there are thick fibers, most of 
which are from the VIIIth root. Those which have already 
crossed the mid-line are cut longitudinally (Xed.VIJI); the un- 
crossed VIII th root fibers are cut transversely. The latter form 
a fascicle of very thick fibers and are characteristic of Ameiurus. 
They ascend from the root of the same side and at the level of 
Mauthner’s cell turn rostrally, giving off collaterals to the cap 
through its entire extent. As the figure shows, there are two 
kinds of terminations in the cap, the fine free endings and the 
knob endings (K.End.), the latter in contact with the surface of 
the cell. This point is evident in figures 11 and 12, which are 
taken from a brain fixed in formol-osmic-Zenker, a fixation which 
produces less distortion and shrinkage in this material than any 
