PRENTIsS, Neurofibrillar Structures. 163 
Material and Methods. 
The ventral ganglia of the leech (Hrudo medicinalis) and 
the abdominal ganglia of the crayfish (Astacus fluviatilis) formed 
the material on which most of my study was based. A part of 
the Hzrudo material was treated as described in my former 
paper (PRENTISS, : 03), the method being based on that of 
BETHE (: 00a). Sections 10u thick, fixed in corrosive sublimate 
were impregnated with ammonium molybdate solution (1:4000- 
1:6000), differentiated about one minute in warm water (55°— 
60° C) and then stained with an aqueous solution of toluidin 
blue (1:3000). Inthe ganglion cells a pure fibrillar stain was 
obtained by fixing ganglia for one hour in ether fumes, staining 
zm toto with toluidin blue (1:3000) and fixing the stain ina 1% 
solution of ammonium molybdate. The material was then 
dehydrated, embedded in paraffin and sectioned in the usual 
manner. This method is simple, but uncertain in its results. It 
is a selective method, like methylen blue, and not all of the 
fibrillae are demonstrated. Often, however, preparations were 
obtained which showed the fibrillae with diagrammatic dis- 
tinctness. 
The preparations of Asz/acus material were all stained zntra 
vitam with methylen blue. The fibrillae were differentiated by 
leaving the ganglia 2-4 hours in normal salt solution ; the stain 
was then fixed in ammonium picrate, which differentiates the 
fibrillae more clearly than molybdate. 
The Fibrillae in the Ganglhon Cells. 
ApATHY describes two types of cells in the ventral ganglia 
of Hirudo, distinguished from each other by their size and the 
structure of the neurofibrillae. In the type to which the 
smaller cells belong, one large fibril enters the cell and forms a 
close meshwork of rather large fibrillae about the nucleus. 
This is a motor or cellulifugal fibril according to APATHY; its 
network about the nucleus is connected by radial fibrils with a 
finer peripheral meshwork formed by smaller cellulipetal or 
sensory fibrillae. In this manner he assumes that sensory and 
motor elements are put into direct communication within the 
