86 W. N. F. WOODLAND 
absent) and are radially subdivided by the numerous con- 
nective tissue septa above deseribed. Forming the central 
axis of the regenerated tail is a thick-walled cartilaginous 
tube (Text-fig. 4, ©). The cartilage of this tube is calcified * 
on its outer surface (next the fat bands) and on its mner 
surface (next the spinal canal), the space between these two 
concentric cylinders of calcified cartilage consisting of ordinary 
unealeified cartilage. Anteriorly this cartilaginous tube joins 
on to the ring of bony tissue formed by the centrum and 
neural arch of the last vertebra (Text-fig. 2, C) and so secures 
a continuation of the spinal canal. The cartilaginous tube is 
quite continuous—no planes of cleavage being present—and 
it bears no processes of any kind, neural spines and haemal 
arches both being absent. The contents of the cartilaginous 
tube are (a) a very attenuated extension of the spinal cord 
(about a quarter or less of the diameter of the original) which 
practically consists of a continuation of the cellular lining of 
the canalis centralis, with little or none of the external nerve- 
fibre substance ; (b) a network of capillaries which hes for the 
most part ventrally to the spimal cord extension ; and (¢) an 
arachnoid meshwork contaiming pigment cells. In view of the 
fact that no nerves are given off from this slender extension of 
the spinal cord into the regenerated tail, it 1s evidently quite 
a useless structure so far as muscular innervation is concerned ; 
it, however, contains a well-developed Reissner’s fibre (‘Text- 
fig. 4, D). It may here be mentioned that the nerves supplying 
the slender muscle bands are all derived from the last two or 
three pairs (I have not determined the exact number) of nerve 
roots in the stump of the original tail (according to Powell 
White, the nerves are, n Lacerta vivipara, derived 
from the last three pairs) and, as stated, have no connexion 
with the regencrated spinal cord. In the abstract of Powell 
White’s paper it is stated that in Lacerta viridis the 
cartilagimous tube enclosing the spinal cord is ‘ unseemented 
1 This calcification of the cartilage is apparent in thick unstained hand- 
cut sections of aceto-bichromate-fixed material ; in ordinary microtome 
sections it is not easily scen, 
