I1O JouRNAL OF COMPARATIVE NEUROLOGY. 
one large nucleolus, with a subsidiary nucleolus in some cells. 
The nuclear reticulum has a rather fine mesh; large granules 
of chromatin occur at the points of intersection. 
The dendrites arise from the peripheral side of the cell- 
body, and they pass at once into the molecular layer, taking a 
direct course for the limitans externa. The size of a dendrite 
is maintained without marked diminution, the tip, in fact, being 
so large and blunt as to givea club-like appearance to the 
whole process. The mode of branching is far simpler than that 
of the corresponding mammalian neurone. While the dendrite 
of the latter ramifies to an extraordinary degree, it is rare to 
find branching carried beyond the tertiary divisions in Mustelus; 
compare my Fig. 13 with Plates 14 and 15 of Srarr’s Atlas 
(96). From its greater simplicity, the selachian neurone of 
PURKINJE corresponds, in a broad way, to the embryonic condi- 
tion of the higher form. The branches are spread in one plane, 
like a plant trained on a wall, and this plane lies transversely to 
the cerebellar folds. The course of the branches in this plane 
is less wide than for mammals, causing the whole top to present 
a markedly more compact appearance. The surface of a den- 
drite has the conspicuous roughness characteristic of this neu- 
rone wherever found. The gemmules, to which this roughened 
surface is due, are of several different sizes, ranging from 
mere points through slender spines and stouter thorns to knobs 
and mushroom-like excrescences which rise far above the gen- 
eral level. The extent of receptive surface of the entire den- 
dritic series is thus increased to a very considerable degree. 
The part which the neurone of PuRKINJE takes in the econ- 
omy of Mustelus will be discussed in Subsection 5. 
2. The Molecular Layer. 
This is the external layer of the cerebellum (Fig. 12, . /.). 
It conforms throughout to the contour of the several folds into 
which the cerebellar wall is thrown. Its thickness is carried — 
with considerable uniformity, but in most of the regions the 
depth of matter is only about half as much as that of the gran- 
ular layer within. 
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