238 
EDWIN S. GOODUICH. 
but reverse process of reduction, a limb originally supplied b}^ 
nerves c-J may come to be supplied only by nerves e f g. 
If such were really the case we should expect to find the limits 
of a plexus somewhat indefinite and variable, the moro 
important and stouter nerves towards the middle, aud slenderer 
twigs contributed by nerves at each end. Now this is just 
what anatomical investigation reveals; a limb-plexus is built 
on this plan. 
Further, a limb-plexus may shift, without altering its general 
structure, from one region to another, by such a process of 
growth or extension at one end accompanied by reduction at 
the other end. New segments being assimilated along the 
direction of growth, others may drop out, ceasing to contribute 
to the plexus. Thus a nerve-plexus may successively occupy 
segments n e f, e f g, f g h, and G h J. By a gradual 
process a plexus comes to occupy an entirely new position, 
having been transposed without the appearance or disappear- 
ance of any segments at all. What is true of the nerves is- 
doubtless true also of the musculature and skeletal elements 
(Diagram 5). The fact that the position of a nerve-plexus and 
the size of its component nerves is an accurate guide to the 
segmental composition of a limb has already been sufficiently 
dwelt upon above. 
This theory of the shifting of a plexus and a limb from ona 
region to another is in complete harmony with the teaching 
of comparative anatomy and embryology. It is the only 
theory which gives a reasonable explanation of such cases as 
Baja and Gadus, and the independent motion of the paired 
and unpaired fins mentioned above. The process whereby 
the transposition^ is brought about may be interpreted as due 
neither to the insertion or removal of segments nor to the 
' To the correspondence between two similar sets of nerves forming a 
plexus, but occupying different ordinal positions in the series of 
segments, Fiirbringer has applied the word Parhomology. This term,, 
however, seems to imply that the homology is incomplete, whereas it is 
here contended that it may be as complete as between any two organs. 
Fiirbinger also applies the term “ imitative honiodynamy ” to the 
