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CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 81 
and only then able to effect the disruption of the feeble anterior 
attachments of the muscles. Disruption of the muscles having 
occurred on one side (and with it disruption of the skin, fat 
layer, fat bands, and vertebrae along their cleavage planes), 
the muscles of the other side of the segment contract violently 
in their turn and so complete the process of autotomy. This 
interpretation of the action of the muscles in autotomy explains 
why it is that the Gecko cannot shed its tail unless it 1s held,. 
i.e. relatively fixed, a fact which I have already remarked upon. 
A Brier COMPARISON OF THE STRUCTURE OF THE GECKO TAIL 
WITH THAT OF THE Tarn oF A NoN-AuTOTOMOoUS LizARD— 
Calotes versicolor. 
If we examine the tail of a typical non-autotomous lizard, 
such as Calotes versicolor,’ we find conspicuous dif- 
ferences from the Gecko tail. In Calotes the tail is covered 
with equal-sized scales arranged in longitudinal rows, all the 
scales of adjacent longitudinal rows alternating with each other 
in position (Text-fig. 8, M); thus the arrangement of the 
scales shows no signs of segmentation, and lines of cleavage 
are of course absent. The annular arrangement of the scales at 
the ends of the autotomy segments of the Gecko tail must 
therefore have arisen secondarily in relation to autotomy. 
Internally in the Calotes tail, fat layer and fat bands are both 
absent, the entire space between the skin and the vertebral 
column being occupied by muscles.. The general arrangement 
of these muscles, which can be seen when the tail is. skinned 
(Text-fig. 2, N, O) and from transverse sections (‘Text-fig. 8, L), 
is much more complicated than in the Gecko tail. In Calotes 
all the superficial muscles are arranged in a zigzag myotome 
fashion, but those internally situated are continuous (not 
myomeric) and run longitudinally the greater part or the whole 
of the length of the tail. In Varanus a similar arrangement 
of the muscles obtains. From these facts it will appear 
! The cut tails of two Calotes showed no signs of regeneration after one 
anda half months of captivity, and I have never met with a regenerated 
tail in this animal in nature, nor in Varanus. 
NO, 257 G 
