CAUDAL AUTOTOMY AND REGENERATION IN THE GECKO 87 
and continuous except for some perforations through which 
blood-vessels pass to the interior’. In the fully-regenerated 
tail of the Gecko no perforations at all exist in the length of 
the tube, not even for blood-vessels, though perforations (for 
vessels) are fairly numerous in the young growing 
cartilaginous tube, and I suspect that this is also the case in 
Lacerta. It certainly is so in Pygopus, sections of which 
Professor J. P. Hill has kindly shown to me. At the extreme 
posterior end, however, of the cartilaginous tube in one series 
of sections of a fully-developed regenerated tail I have found 
one median ventral terminal opening and two lateral sub- 
terminal openings through which blood-vessels pass, but these 
are the only openings I have discovered. In another series of 
sections of a young regenerated tail (6 mm. in length) I found 
that the spinal cord continuation actually bifurcated at its 
posterior extremity, one branch piercing the cartilaginous tube 
through a mid-ventral subterminal opening, the other branch 
continuing to the end of the tube, but I suspect this to be 
a freak. 
The caudal artery extends back into the regenerated tail 
lying underneath the cartilaginous tube, and only differs from 
that of the original tail in not being enclosed in a haemal canal 
and in being devoid of sphincters; it gives off branches at 
intervals. The caudal vein extends posteriorly under the 
caudal artery and is uniform in diameter. 
Tur HistoGEnesis oF NorMAL CAuDAL REGENERATION. 
Under this heading I can only confirm and correct previous 
accounts. As Powell White says, “The wound after autotomy 
is quickly covered with new skin [not derived from the old 
skin covering the stump of the original tail], beneath which is 
a mass of spindle cells | quasi-embryonic tissue] which apparently 
originates in the connective tissue. This cellular mass acts as 
a growing-point to the new tail, and from it the various struc- 
tures are developed. The cartilage, fat, and blood-vessels 
arise by differentiation from the spindle cells. The muscle 
fibres arise segmentally in groups, the groups nearest the tip 
