670 
of the volumes of the nerve cells, as would be the case when the 
neurones were similar in form. 
In other cases of dissimilarity in form the comparative length of 
homologous nerve fibers in the large species is smaller than in the 
case of conformity. But with all differences of the relative length 
and section of the nerve fibers the relation between the volumes of 
the neurones and their ganglion cells yet remains the same. We 
always find: 
(= oN 
C, mi N, 
and the volume of homologous ganglion cells always varies. in pro- 
portion to the power 0.27 or 9/8 of the body weight: 
CPN 
o-r) 
If this power were 0.33 or 6/18, its meaning would be clear at 
once. For the movements of animal species of the same form, but 
of different sizes, are slower, and the muscular contractions more 
prolonged, in proportion to the greater length of the body, the result 
being that large and small animals move along equally rapidly. The 
Tiger, e.g., moves at the same speed as the Cat, but with slower 
steps. It would be natural to conclude to a corresponding variation 
in the volume of the ganglion cells supplying the stimulation energy. 
D 
P Ns 
The proportion found departs little from (=) , but the deviation 
1 
is constant, and has, accordingly, a rational significance. This opinion 
is supported by the fact that the area of the retina varies in the 
\5 
same way, in proportion to (=) is The comparison of the receptive 
1 
cells of the retina with the ganglion cells of the brain is certainly 
reasonable, on account of the origin of this membrane as a bulging 
out of the primitive cerebral vesicle; the retina is actually a complex 
of neurones. But then it follows that the area of the retina must 
vary to the same degree as the nerve cell vo/wme. In animal species 
of different sizes the impressions of the retina (images) vary with 
its area; those of the nerve cells of the spinal cord and the brain 
with the volumes of the cells. In the retina the area of the cross 
section and the volume of the receptive elements must vary to the 
same degree *). 
1) The available data are not sufficient to allow us to judge about the variation 
of the area of the cross section of the receptive retina-elements with the body 
weight of homoneuric animal species. GisA ALEXANDER ScHärer (Pflügers Archiv. 
