468 BUMPUS. [Vor xil 
itself ;$, or ;4 of the measured distance. But the verte- 
bree in the region of the selected intervertebral spaces are, in 
length, considerably less than ;4, the measured distance; 
so that the oscillations of the dividing line between the XIX 
and XX vertebrz would be such as to carry it back and forth 
over a distance greater than one vertebra anteriorly and one 
posteriorly. 
If we should string a series of thirty short segments of rub- 
ber tubing upon a cord, and then, after placing a card between 
the XIX and XX, subject the entire series to slight pressure, 
we would have what might roughly correspond to the column 
under consideration. The card, representing the selected in- 
tervertebral space, can be forced forward or backward over a 
certain amplitude, according to the compressibility and elas- 
ticity of the rubber rings. Suppose, while the card is at rest, we 
hold two fingers of the hand in such a position as to represent 
the rudiments of the appendages, lying on either side of the 
nineteenth ring. Now when the card is forced anteriorly the 
fingers lie no longer opposite the XIX, but opposite the XX 
vertebra. A forward homeeosis has taken place illustrative 
of what happens in a large per cent of the specimens of 
Necturus. 
But do our data warrant the assumption that with the com- 
pression of the anterior vertebrz there is a concomitant varia- 
tion in the position of the hind limbs? When specimens tend 
toward elongation of the caudal region, do the legs appear on 
the XX, and when the reverse obtains do they tend to arise 
from the XIX vertebra? 
A further examination of the plate will answer in a most 
conclusive way. 
Specimens No. 58, 61, and 74 have the greatest elongation 
of the posterior vertebrze, and in every one of these specimens 
the sacral ribs are borne by the XX vertebra. 
In other words, in all the specimens presenting extreme 
compression of the anterior vertebrz there is concomitant 
variation in the position of the hind limb. 
Arranged on the abscissa of 34% (Plate C) are thirty-two 
specimens, and, if our theory is to be supported, a less number 
