162 University of California Publications. [zoology. 



nature presented by two of the species under consideration, 

 namely, the capacity for autotomy of the tail. Batrachoseps 

 drops its tail very readily and on slight provocation, the break 

 occurring at almost any point. It also regenerates this organ. 

 Diemyctylus does not shed its tail. Plethodon stands between 

 Batrachoseps and Diemyctylus in this respect, for though it can 

 and does part with the member, it does this only under stress 

 of the most untoward circumstances. Holding the animal by 

 the tail, irritating it with acid or by an electric current produces 

 no effect. It was not until individuals were put tail foremost, 

 half way down the throat of a snake, that they finally parted 

 with their caudal appendages, and it actually took four encounters 

 with a ring-necked snake to bring off the tail in one specimen. 

 Thus it would appear that Plethodon reserves this act of autotomy 

 as a last resort, using it only when nothing else avails. 



As has been said, the break in the tail of Bati-achoseps occurs 

 at any point. In Plethodon, on the other hand, so far as direct 

 observation has gone, it comes only at the constriction behind the 

 anus. Thus it took place here in three individuals which shed 

 their tails in the terrarium, in two which were held in the throat 

 of a snake, in one which was attacked by a snake, and it was seen 

 in another which had been regurgitated. It oecui-red here in an 

 individual which was placed in the killing fluid without a previous 

 anaesthetic, and in numerous museum specimens, probably killed 

 in the same way, the tail showed a weakness in this spot, breaking 

 here very readily. Three specimens from the field were regener- 

 ating the organ from this point. In one case only did there seem 

 to be an exception to this rule, and that was in an individual 

 which was regenerating the tail at a point somewhat more than 

 a centimeter from the anus, as shown in fig. 3, PI. XVI. But 

 this exception is of doubtful significance, for the tail may have 

 suffered some accident or been bitten off, though it seems some- 

 what inconsistent with the general conclusion to suppose that 

 the animal would permit this loss in preference to parting with 

 the whole organ. 



Dissection shows that the division occurs simply by an 

 unlocking of the vertebra', not by a break in the centrum, as in 

 the case of self-amputation of the lizard's tail. 



