CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 83 
with those separating the other tissue of adjacent segments ; 
also the plane of cleavage lies immediately behind the trans- 
verse process of the centrum, which is therefore not affected 
by autotomy and remains projecting from the posterior surface 
of the portion of tail retained by the animal (Text-fig. 1, F). 
I have verified these statements in numerous longitudinal and 
transverse microtome sections, also in hand-cut scetions, these 
latter proving, in virtue of their thickness, more useful on the 
whole than the former. 
I may add here that there is apparently great general 
similarity between these cleavage planes in the Gecko tail and 
the ‘ breaking plane’ which Paul! has recently described in 
detail in Decapod’ Crustacea. In fact the only conspicuous 
difference between the two is as regards number—in the 
Crustacean there is only one plane for each limb, whereas in 
the Gecko (as in the Ophivroid arm) there are as many planes 
as there are jomts. And just as there is a sphincter on the 
Gecko caudal artery to stop haemorrhage, so in the Crustacean 
there is a diaphragm developed for the same purpose. In all 
cases muscular action affects autotomy of the shed part along 
the cleavage plane. 
THE STRUCTURE OF THE REGENERATED TAIL OF THE GECKO. 
The most conspicuous difference between the regenerated 
tail and the original tail is the total absence of any signs of 
segmentation in the former, either on the surface or in internal 
structure. On the dorsal surface of the tail the skin bears 
a uniform covering of the usual small scales (Text-fig. 1, C, D), 
i.e. the smal! scales are arranged in the same somewhat irregular 
manner throughout the length of the tail, and no larger scales 
are present. Qn the sides of the tail the scales are larger, and 
on the median ventral surface there is a longitudinal series 
of large laterally-elongated scales (Text-fig. 1, HE). The sub- 
cutaneous fat layer is present (Text-fig. 4, A), very thin dorsally 
' “ Regeneration of the Legs of Decapod Crustacea from the Preformed 
Breaking Plane”, J. H. Paul, * Proc. Royal Soc., Edinburgh’, vol. xxxv, 
1914-15, p. 78. 
G2 
