CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 8&9 
exposed by the cut, the endoskeleton of the regenerated tail 
was of the normal cartilaginous tube type. These experiments 
also prove that the tissues bordermg the autotomy plane are 
not indispensable for the regeneration of the tail—histogenetic 
cells are distributed throughout the tail tissues. I may add 
that in one of these four experiments I held the animal by the 
regenerated tail (of 66 days growth) but I could not induce 
autotomy either from the junction of the regenerated tail with 
the original stump or from a true autotomy plane anterior to it. 
Regeneration from the Cut Base of the Tail. 
I have stated that the first autotomy plane in the Gecko tail 
is situated between the posterior surface of the base of the tail 
and the anterior surface of the first autotomy segment. Since 
we now know that caudal regeneration can occur at the surface 
of any autotomy segment cut intervertebrally, 1.e. between 
two successive autotomy planes, it is of interest to imquire 
whether regeneration can occur from the posterior surface of 
the base of the tail if this be cut through anterior to the 
first autotomy plane. ‘The answer to this question 
is also of special interest when we reflect that the structure 
of the base of the tail is different in several respects from that 
of the segmented tail proper—in the absence of segmentation, 
in the absence of fat bands, and in the arrangement of the 
muscles—and that it has been contended that (in the Gecko 
and the other Lacertilia which it resembles in this respect) the 
regenerated tail differs in type from the original tail solely 
because in development the former is shut off from the con- 
trolling influence of the main organism by the hyaline septa 
of the autotomy planes, whereas the original tail is developed 
before autotomy planes (which are only produced after the 
original tail is formed) are present. 
I performed this experiment of cutting through the base of 
the tail four times in 1914 but in no instance did regeneration 
occur, though the Geckos were kept for two months. In 1918, 
however, when I repeated the experiment, five of the Geckos 
regenerated tails of the normal regenerate type 
(Text-fig. 5, A’, A”), as shown by the cartilaginous tube, fatty 
