The Morphology of Functional Activity in the Ganglion Gells etc. 547 
to be regarded as final, though by its repetition in the conrse of a life 
it may ulthnately become so. There are types of cells whicli are inter- 
preted as recovering and the occnrrence of recovery is predicated by 
analogy and by comparison of cell States in yonng and old aniinals and 
at different seasons. 
Conclusions. 
The folloAving conclusions are drawii from this and previous Avork. 
On the histological side: 
1. Applying the variations due to cellular actmty in conjunction 
Avith the findings of Retzius as to the arrangement and distribution of 
fibres in Astacus fluviatilis, the neui’ons composing the nervous System 
of Cambarus virilis consist simply and essentially of a motor and a sensory 
group, each of Avhich may be divided into a purely central and a centro- 
peripheral sub-group. A fifth order of cells common to aU ganglia A\'as 
determined from them size and different nucleus-plasma norm Avhich is 
probably purely associational in function, though the possibility of a 
greater complexity of its components has not beeil eliminated for aU 
ganglia. 
2. The number of cells of a given type in a ganglion has been found 
to an extent Avorthy of note to be a constant for aU animals of the species 
studied. 
Regarding the nucleus-plasma relation: 
1. For resting cells, of both sensory and motor types, in Cambarus 
virilis, there is a definite relation of nuclear mass to ceU mass. 
The coefficient of this relation is an identical constant both aniong 
the four types of primal resting ceUs in the same animal and for all anhnals 
of the species, Avhatever their size. 
2. From these results on the primitive ceUs of Cambarus virilis and 
from the same constancy and uniformity of the relation in indmdual 
and species Avhich holds for the resting Purkinje cell of mammals as a 
type of most highly differentiated ceU Avithin each of the three species 
studied as elscAvhere presented, the application of Richard Hertwig’s 
nucleus-plasma relation theory appears in conjunction Avith other evidence 
to be demonstrated for all nerve cells. 
3. As a residt of functional activity, the same constant and orderly 
shifts and final upset of this relation occur in aU ceUs in aU animals of 
the species Cambarus virilis. 
4. The coiu’se of the functional upset duplicates in essential detail 
the course of the Purkinje cell. This is fiu’ther evidence for the universal 
