CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 67 
bending it at one point laterally), but was a result of powerful 
localized contraction of the tail muscles causing sudden flexion 
at one point. These observations prove that autotomy is 
a purely voluntary process, and this is confirmed by the 
further fact that Geckos, caught by the tail, sometimes refuse 
to autotomize when they perceive that escape is impossible 
(compare the refusal even to attempt to fill the gas bladder 
with more oxygen when a fish is over-weighted!). On one 
occasion a Gecko, tied up by thread, remained captive for 
three days, though it frequently tried to run away when 
I approached, and it was only when I held the tip of the tail 
that autotomy occurred—apparently the fulerum provided by 
the cotton attachment was insufficient in this case. 
(3) The original (non-regenerated) tail of H.flaviviridis 
consists of a basal unsegmented region (the * base’) covered 
only with small inconspicuous scales, and about thirty autotomy 
segments, each of which can be distinguished dorsally (Text- 
fig. 1, A, D) by the presence on its extreme posterior edge of 
six large projecting scales (three on each side of the middle line), 
the outermost scale on each side being the largest ; ventrally 
each segment extends lengthwise over two of the large median 
transversely-elongated flat scales (Text-fig. 1, B, EK). As 
experiments prove, autotomy can occur at the posterior edge 
of the base of the tail or of any subsequent segment, but 
cannot occur in front of the posterior border of the base. 
In fifty captured specimens I have found examples of autotomy 
having occurred naturally at every segment situated between 
the base of the tail and the sixteenth segment: thus in seven 
specimens. autotomy had occurred at the posterior edge of the 
base, 1.e. the whole of the segmented tail had been shed ; in 
ten specimens autotomy had occurred between the first and 
second segments, and so on, the examples decreasing in number 
the more posteriorly situated the site of autotomy. In nature 
autotomy usually occurs in the anterior half of the segmented 
region (Text-fig. 1, D, HE), but may of course also occur pos- 
teriorly to this. 
1 Woodland, W. N. F., ‘ Anat. Anzeig.’, Bd. XL, 1911, p. 225. 
F 2 
