CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 97 
bands have degenerated into the fat bands and become 
secondarily segmented. 
4. The autotomy planes are marked by simple septa of a 
hyaline matrix.bordered by connective tissue, which traverse 
and separate into segments the entire substance of the tail. 
The spinal cord, nerves, and blood-vessels are, however, con- 
tinuous. 
5. The structure of the regenerated tail is described. Reiss- 
ner’s fibre is present in the regenerated spinal cord, as in the 
cord of the original tail. Boulenger’s explanation of the 
changed character of the lepidosis of the regenerated tail when 
compared with that of the original tail, viz. that it is a reversion 
to an ancestral type, does not apply to the internal anatomical 
features which distinguish the regenerated from the original 
tail. A more probable explanation of the differences between 
the regenerated and original tails is that the former, being 
merely produced for autotomy purposes, is ‘jerry-built ’"—an 
appropriate description of a tail in which the muscles have no 
direct connexion with the endoskeleton and the spinal cord is 
devoid of nerves, ganglion cells, and fibres. 
6. Tails of the normal regenerated type can be produced 
from cut surfaces situated between the autotomy planes and 
anterior to the first autotomy plane in the base of the tail. 
This is proof (a) that the histogenetic cells occur throughout 
the tail substance and quite apart from the hyaline septa, 
(b) that the peculiar features of the regenerated tail are not 
due to a lack of organic connexion with the rest of the body 
caused by the interposition of the autotomy plane septa. 
7. The axis of the regenerated tail usually tends to be 
placed at right angles to the plane of the cut on the tail stump. 
In four of my experiments accessory tails were produced, none 
of which contained a cartilaginous tube endoskeleton. 
8. The tails of Pygopus and Lacerta viridis are ap- 
parently almost identical in structure with those of the Gecko, 
and in Sphenodon punctatus the tails only differ 
essentially in the absence of the fat bands and the absence of 
sphincters on the caudal artery. 
NO. 257 H 
