The visceral ganglion of Pecten, etc. 
11 
ganglion is not thick enough in Pecten to allow a definite Separation of 
cells in this way, but neuroglia cells occur in the sheath, with nuclei 
and fibres of the surrounding connective tissue, and they are particu- 
larly abundant on its internai surface and around the most peripheral 
ganghon cells. 
The neuroglia fibres can be traced easily in the ganghon celi cortex, 
where they separate and enclose the individuai cells in a kind of network 
and finally nuclei and neuroglia fibres occur in the neuropil and the nerves. 
The shape of the neuroglia cells is not to be made out from sections and 
the cytoplasm surrounding the nucleus is not easily stained. The nuclei 
(fig. 11 Gl.n) are very conspicuous and stain more deeply than the nuclei 
of the nervo cells. They are much smaller than the latter, usually ellip- 
soidal in shape with a length of about 6 ^i. They contain numerous 
chromatin granules but a distinct nucleolus is never visible. There is 
very little protoplasm surrounding the nucleus and from this perinu- 
clear protoplasm arise long fibrelike processes which may brauch (fig. 
11 Ol.f and fig. 12). The cells may be multipolar or as is the case in 
the nervo fibres more generally bipolar. As stated above there is a 
perfect network of fibres enclosing the ganglion cells (fig. 12) but the 
thickness of this neurogha sheath is less than that of Eelix or Octopus. 
The cortical neurogha is best developed in the dorso-central lobes, where 
also are to be found the projections of the ground substance of the ganghon 
sheath. The neuroglial fibres do not penetrate the ganglion cells, as 
they do in Helix, though in some cases, they may be traced into the 
peripheral layer of the celi (fig. 11). The neuroglia nuclei in the neuropil 
and nerves are identical. They were regarded by Rawitz as belonging 
to nervo cells, which aided in the formation of the neuropil and are termed 
»Schaltzellen« by him. List refers to some small nuclei in the nerves 
which he terms connective tissue nuclei and to »Nervenzellen« in con- 
tradistinction to ganglion cells. I caunot find them indicated in his 
figures. It may be mentioned here that in Pecten the connectives and 
peripheral nerves in the vicinity of the visceral ganglion contain only 
nuclei of non-nervous cells, with the exception of the branchial and os- 
phradial nerves which contain ganglion cells. In Venus Casina the cerebro- 
visceral connective contains one or two scattered ganglion cells, in Ensis 
ensis none were to be seen. In those lamellibranchs examined (see 
pag. 26) the branchial nerves were distinguished in ali cases by a cortex 
of ganghon cells, and if nervo ceUs occurred in the other nerves or connec- 
tives, they were very few in number and scattered, (except in Mya trun- 
cata about which I shall have something to say in a later paper). 
