MAUTHNER’S CELL 107 
other [ have found. We may safely assume that the form rela- 
tions’in this preparation are more nearly true to life than they 
are in Cajal preparations; a comparison of the collaterals arising 
from the large VIIIth fibers of the axone cap in figures 10 and 12 
is particularly illuminating in this connection. It need hardly 
be said, however, that the details shown in figure 12 could hardly 
be interpreted if one had not first studied the more obvious pic- 
tures given by Cajal preparations. Besides the collaterals from 
_ the VIIIth root fibers, numerous collaterals are given off from 
the secondary VIIIth fibers (fig. 10) as they stream past Mauth- 
ner’s cell before crossing the mid-line to ascend as the acoustic 
lemniscus. 
Fibers from the fasciculus longitudinalis medialis are almost as 
numerous as those from the VIIIth roots. They seem for the 
most part uncrossed and are gathered into two bundles. One 
of these consists of fine fibers from the infracommissural bundle 
of the tract which enter the axone cap ventro-medially. A few 
of them are shown in figure 10 (Col.F.L.M.), where their small 
size as compared with the VIII th roots fibers is apparent. They 
stand out clearly in hematoxylin preparations as a loose bundle 
of unmedullated fibers and are doubtless collaterals from descend- 
ing fibers. The other bundle of fibers is unique; it has not been 
recognized hitherto in fishes, but C. J. Herrick (’14) has described 
it in Amblystoma and I have found indubitable evidence for it 
only in osmic acid preparations. It is a bundle of small medul- 
lated fibers which can be traced with a fair degree of certainty 
from the mesencephalic nucleus of the fasciculus longitudinalis 
medialis. It leaves the supracommissural bundle of the homo- 
lateral tract, where Mauthner’s fiber swings around it (figs. 3 
and 6), and envelops the fiber to the point where it emerges from 
the axone cap. Here its fibers lose their sheaths and ramify as 
iree endings in the cap. , 
Most of the endings in this extraordinary synapse may be 
grouped in one of three classes: fibers from the fasciculus longi- 
tudinalis medialis, collaterals from the secondary acoustico-lat- 
eral tract and, most important, collaterals of VIIIth root fibers 
from the same and the opposite side. The predominence of the 
