96 W. N. F. WOODLAND 
connective tissue by means of the radiating septa separating 
the muscle bands. ‘The tails of Sphenodon, therefore, appear 
to be less specialized for autotomy than the tails of the Gecko, 
though the presence of definite autotomy planes, the evident 
simplification of the muscles, and the presence of the carti- 
laginous tube indicate that considerable progress has been made 
in that direction. 
ResuME. 
1. The Gecko original tailis made up of numerous (about thirty) 
autotomy segments, separated from each other by as many 
hyaline septa marking autotomy or cleavage planes. Autotomy 
ean occur voluntarily at any plane provided that the tail be 
held a short distance posteriorly to the point of separation. 
Autotomy in the Gecko is never ‘ spontaneous’ or the result 
of mere alarm. 
2. The structure of the original Gecko tail is described. 
The caudal artery develops a sphincter muscle in its walls 
immediately anterior to each autotomy plane as a means of 
avoiding haemorrhage after autotomy. J am not aware that 
a sphincter muscle has previously been described in connexion 
with a blood-vessel. The caudal vem is similarly constricted 
in front of each autotomy plane. The base of the tail differs 
from the segmented portion in the absence of fat bands and 
in the arrangement of the muscles. The flexor muscles of each 
tail segment are firmly attached posteriorly to the vertebra 
and the outer surface of the fat bands; anteriorly, however, 
they are only attached to the connective tissue of the hyaline 
matrix in the autotomy plane and are threfore easily separated. 
Autotomy is effected by the strong localized contraction of 
these muscles separating their weak anterior attachment. 
3. Comparison of the Gecko tail with the non-autotomous 
tail of Calotes shows that in order to effect autotomy the former 
has become greatly simplified. The scales have become 
rearranged at the extremities of each autotomy segment, the 
superficial museles have also become rearranged on a more 
simple plan, and the internal longitudinal continuous muscle 
