(2 W. N. F. WOODLAND 
when progression is seen to be effected mostly by undulations 
of the trunk, the tail only waving as an appendage of the 
trunk), nor for leverage (like the tails of hounds in turning 
corners), nor for balancing (lizards with amputated tails 
appear to be at no disadvantage in climbing or running), nor 
for means of offence (I have chased large Monitors in the 
jungles on the south coast of Ceylon and in southern India 
and on no occasion have they attempted to strike with their 
tails, though they can lash them) ; on the other hand, the tail 
must often be a positive disadvantage, since it 1s easy to catch 
most lizards by their tails. It is also a fact that m many 
lizards the tail muscles are more or less degenerate (the white 
muscles being valued as food in many cases), or at least Incapable 
of exerting much force (in Central India the snake-charmers tie, 
without cord, the tails of small Monitors in loops round their 
necks, the bases of the tails then serving as convenient handles!). 
These bemg the facts, it 1s not surprising that numerous 
Lacertilia have discovered in their tails, otherwise useless and 
indeed a danger, a means of self-preservation by the adoption 
of caudal autotomy. As we shall see in the Gecko, the whole 
structure of the tail 1s adapted for autotomy at every joint, 
and if, after describing these adaptations, we glance at the 
structure of the tails of lizards which are non-autotomous 
(e. g. Calotes), we shall appreciate the considerable simplification 
of structure which must have taken place in the ancestors of 
the Gecko in order to produce an autotomous tail. 
If we examine longitudinal (‘T'ext-fig. 2, A, C) and transverse 
(‘T'ext-fig. 2, B) sections of the original Gecko tail we shall 
observe the following features. (a) The skin is divided into 
cylindrical regions, each covering one complete autotomy 
segment, by lines of cleavage (described in detail later), 
each of which extends round the entire circumference of the 
tail, and the small scales forming the uniform covering of the 
skin are arranged (‘Text-fig. 2, A) in correspondence with these 
regions : at the anterior or posterior edge of the region bordermg 
the line of cleavage the small scales are arranged in a transverse 
circumferential line, whereas in the space between the lines 
