- Houser, Zhe Neurones of a Selachian. 97 
These axones are strikingly conspicuous structures when suc- 
cessfully impregnated with chrome-silver. 
A second form of neurone is considerably larger in size, 
its dendrites enter into the tangle referred’ to, instead of ‘its 
axone. From a polygonal cell-body, some three or four den- 
drites radiate indifferently in all directions. The dendrite is of 
fine calibre, and it branches repeatedly into ever finer twigs. 
The branching of this system is far less profuse, however, than 
that of the axone of the first variety described. The difference 
will be readily seen by reference to Fig. 5, 0. The axone takes 
a course out of the gelatinous substance into the deeper parts 
of the nucleus. It gives off a number of long collaterals during 
that part of its course lying in the substantia gelatinosa. 
The two kinds of neurones just described evidently con- 
stitute the physical basis for the central reception of general 
cutaneous impressions. The first variety, with its short axone, 
is so concerned entirely, it would seem; while the second one 
described, having its axone proceeding to deeper regions, is 
probably involved to an equal degree in both the reception of 
impressions and in their distribution to deeper levels. 
Still a third type of neurone remains to be described (Fig. 
5, ¢.). From an oval cell-body, a few sparsely branching den- 
drites arise which lead far out into the surrounding field. The 
axone takes a course into the deeper nervous matter, giving off 
only a few collaterals. This form of neurone is found outside 
the margins of the groups, and apparently is purely associative 
in function. 
c. Lhe Deeper Neurones.—The deeper parts of the general 
cutaneous nucleus are occupied by fibres having courses in sev- 
eral different directions, and by the bundles of the spinal V 
tract. Neurones are scattered at intervals between the nerve- 
fibres, with a somewhat more closely crowded area just dorsal 
to the lobus vagi. Neuroglia is especially abundant in all parts 
of the nucleus, providing a support for the intricate maze of 
nervous structures. 
The external morphology of a neurone from the middle 
region of the nucleus is shown in Fig. 6. Such a neurone is 
