66 W. N. F. WOODLAND 
mere alarm.’ This I have proved repeatedly by catching the 
animals by parts of the body other than the tail. Further, 
mere lateral flexion (the tail is not flexed to any extent dorso- 
ventrally) of the tail is insufficient to cause autotomy, as may 
be seen when, on being chloroformed, the animal lashes its tail 
vigorously. In fact, an all-essential condition for caudal 
autotomy is that the tail should be held’a little distance 
posteriorly to the plane at which autotomy is to occur, a ful- 
crum thus being provided for the action of the muscles. I have 
proved this by anaesthetizing (with ether) a number of Geckos 
and tying cotton thread round the tail in different positions, 
the other end of the thread being fixed. On recovering from 
the ether, the captive Gecko would at first try to run away 
(though quite unalarmed, since I observed it from a good 
distance away) and only find itself a prisoner by the cotton 
becoming taut It would then, after several further attempts 
at escape, suddenly stretch the cotton to its full extent and 
deliberately autotomize one segment in front of the segment 
held by the cotton. This autotomy was not a mere result of 
the longitudinal pull on the tail (it requires a considerable 
force to pull off a portion of the tail in the direction of its 
length,” though the tail can be easily broken off by sharply 
1 Gilbert White, in a foot-note on page 64 of ‘The Natural History of 
Selbourne’, states that,‘ the blind-worm or slow-worm does not need a blow 
to induce it to cast off its tail. A sudden fright is sufficient.’ This is also 
stated to be the case for the American Opheosaurus ventralis, the 
‘glass snake’. If these statements be true (and the extreme brittleness 
of the tail is doubtless correlated with the rigidity of the tail assumed 
when the animal is alarmed, all the muscles contracting strongly), it is 
proof that autotomy is a much easier process in these forms than in 
the Gecko. Such forms as Anolis principalis, the American 
‘Chameleon’, which can usually be captured by seizing the tail, 
the animal only being able to autotomize by a great effort, and 
Uromastix spinipes, which allows its tail to be pulled off rather 
than release its hold on its burrow, on the other hand, lie at the other end 
of the scale. 
2 In six recently killed Geckos, varying in length from 9-9 cm. to 13-4 
cm,, and in body-weight from 2:4 grm. to 5-5 grm., with the cotton thread 
suspending the weight tied midway in the length of the tail (hanging 
vertically), the weights necessary to break the original tail varied between 
54 erm, and 129 grm., as kindly determined for me by Mr. B. K. Bas, M.Sc. 
