10 
W. J. Dakin 
The Neurofibrilla e. An extended research for the neurofibrillae 
was not made but several special methods were tri ed which included 
methylene blue, Paton's modification of Bielschowsky, and List's 
eosin method. Careful differentiation with Haidenhein's iron haema- 
toxylin and toluidin blue were the only successful methods and here 
it was only just possible to make out a very delicate closed net of some 
considerale extent (figs. 10,11 Nf). It was not possible however to 
resolve this into perinuclear and general networks. The fibrils are 
exceedingly fine. As far as I am aware no detailed descriptions exist 
of the neurofibrillae in lamellibranch ganglion cells, though the gastero- 
pods and cephalopods have received some attention. This neurofibril net 
in the ganglion cell, resembles as far as I have been able to foUow it, 
the description of Gariaeff (1909) for the cephalopods. It is of consi- 
derable extent and nearer the periphery of the cell, the fibrils appear 
to run more or less parallel so that a delicate concentric appearance is 
produced (fig. 11 Nf). More specialised work however is necessary for 
the elucidation of these structures. 
No »Saftkanälchen« discovered and found by Holmgren (1900, 
1902) in both vertebrates and invertebrates are to be seen in the ganglion 
cells, and though processes of the neurogha fibres appear in some cases 
to penetrate a very short distance into the peripheral cytoplasm, they 
were never to be traced far into the cells as in cephalopods or Helix. In 
both the gasteropoda and cephalopoda however the ganglion cells are 
larger than those seen in lamellibranchs and the presence of the neu- 
roglia and »Saftkanälchen« may be perhaps related to this. 
The Neuroglia. The neuroglia has for a long time been of questio- 
nable existence in the lamellibranchiata. Rawitz denied its existence 
altogether and does not seem to have seen the nuclei of these cells. List 
does not enter into any details. Several authors have studied this structure 
in the gasteropoda and Gariaeff in Odopus. Rohde (1893, 1895) 
has investigated in particular the dose relation existing between the 
cytoplasm of the ganghon cells and the neuroglia and shown how the 
former is penetrated by the fibres of the latter which also surround the 
cells. 
BocHENEK (1905) was the first to give a definite account of the 
neuroglia in a lamellibranch (Änodon). He states that there are three 
groups of neuroglia cells in the ganglia of this species. The first are situated 
outside the ganglion sheath which is penetrated by the fibres. The cells 
of the second group lie inside the ganglion but in the cortex of gangUon 
cells, whilst the third group occurs in the neuropil. The sheath of the 
