Houser, Zhe Neurones of a Selachian. 117 
toward the surface, for it runs almost parallel with the layer of 
PURKINJE neurones for a short distance; it then turns upward, 
terminating at the limitans externa ina conical expansion. Dur- 
ing the proximal part of its length, it bears fine processes sim- 
ilar to those emerging from the cell-body. The distal part of 
the fibre has a remarkably vast number of fine processes. 
These may remain separate trom each other, but at intervals 
they become matted together so closely that the whole has the 
appearance of felt or even that of a solid. 
The account given by ScHAPER (’98) of what he took to be 
BERGMANN’s fibres does not correspond with my findings in sev- 
eral particulars. This author does not mention the processes 
of the cell-body, nor do his figures show them. It may be that 
his preparations were insufficiently impregnated. Weight is 
given to sucha possibility from the fact that he did not find 
astrocytes at all. It is certainly of some phylogenetic interest 
that BERGMANN’s fibres appear to be derived from astrocytes. I 
have found numerous instances where transitional forms are rec- 
ognizable, linking the extremes of the simple astrocyte with the 
one provided with a long process, the fibre of BERGMANN. 
The position occupied by the cell-body of a BERGMANN’S 
fibre is also significant. KOLLIKER (’96, p. 368) states that at 
birth BERGMANN’s fibres in mammals lie at the boundary of the 
granular and molecular layers, and that during growth they 
normally migrate into the granular layer. Now the permanent 
position of BeRGMANN’s fibre in Mustelus corresponds to the 
embryonic state in the mammal. An additional comparison may 
be instituted regarding the form of the fibre, the adult element 
of Mustelus remaining simple, while the mammalian fibre be- 
comes much branched. That the condition in Mustelus corre- 
sponds to the embryonic stage of development in higher verte- 
brates is, of course, no more than should be expected. 
The physiological interpretation of the cerebellar neuroglia 
is not difficult. The numerous processes from both the astro- 
cytes and BERGMANN’s cells provide a delicate suspensory appa- 
ratus for the neurones of PurKINJE. The great BERGMANN’S 
fibres, reaching upward as they do through the molecular layer, 
