The Morphology of Fimctional Activity in the Ganglion Gells etc. 501 
from the large cells, whether running in the cephalic or caudal direction, 
may branch and both branches reinain on the same side, or the “stem 
process”, the long arm, may cross to rim either way, or the short arm 
only may cross, but the essential point is that these branches run and 
terminate centrally. Allowing for the existence of a sensory and motor 
division, it is apparent that the Classification Retzius recognizes four 
types principally, a central and centro-peripheral sensory and a central 
and centro-peripheral motor. The division by the writer is held to re- 
present the same four groups. At least, this Classification adequately 
fills the requirements upon the basis of general knowledge. 
Again foUowing Retzius in regard to the specific identity as motor 
and sensory, while he leaves it undetermined, he States that a priori it 
may be considered that the greater cells with their usually greater pro- 
cesses are motor, the smaller cells sensory. Further, the structure of 
the protoplasm differs, the larger cells having more thickly distributed 
though finer granulations than the small cells. This observation has 
been confirmed. With the further light thrown by the process of acti- 
vity, therefore, it seems reasonably safe to diagnose the generally larger 
cells with intracellular axones as motor and the generally smaller cells 
lacking in this as sensory. The central motor group is illustrated by 
Figures 1 — 7, the centro-peripheral motor group by Figures 8 — 12, the 
central sensory group by Figures 13 — 17, and the centro-peripheral 
sensory by Figures 18 — 22. The first series is the more complete, while 
in the others the drawings represent early and final stages. 
Finally, the finding by Retzius in some ganglia of large cells with 
peripherally running axones does not predicate an additional type, but 
is brought within the limits of the fourfold division by the great hyper- 
trophy that may occur in the usually smaller peripherally extending cell. 
The vast majority of ceUs at least are unipolar in Cambarus virilis. 
No attention was paid to the possible presence of multipolar ceUs which 
Retzius States also occur in very limited number and definite place in 
Astacus fluviatilis, though not in the first abdominal ganglion. If they 
are present, they would seem to be excluded from the motor group for 
the single process of the motor ceUs with intraceUular axone is to be 
foUowed constantly from within to without the ceU. In the sensory 
types by the stain employed, the fibre is not always though frequently 
apparent. Certainly their possible inclusion makes no difference in the 
general results from the sensory group when compared with the other 
group, that is, no sufficiently striking exceptions to the trend of the 
size changes in any group have been found to note. Still, outside of 
Archiv f. Zellforschung. IX. 34 
