166 University of California Publications. [zoology. 



the point at issue. From this experiment, only one, it is true, 

 but crucial, I judge that the tail glands in this species offer a 

 partial protection to the animal. They may, perhaps by some 

 offensive odor or by some irritating volatile product, ward off an 

 enemy at times. But this means of protection is only partial, 

 as shown by the experiments, for at times not even the taste of 

 the secretion prevents the animal's destruction. 



To summarize the results of the experiments: We have, in 

 these three species, a graduated series so far as the relation of 

 the power of autotomy ami the presence of these poison glands are 

 concerned. Batrachoseps yields comparatively little poisonous 

 secretion when stimulated; Plethodou yields it abundantly on the 

 tail and Diemyctylus pours it out very generally over the dorsal 

 surface of the body. Batrachoseps is eaten with avidity by 

 snakes. Plethodon is not rejected, but Diemyctylus seems not 

 to be taken at all as food. In Batrachoseps, where the secretion 

 is slight, autotomy occurs on little provocation ami at almost 

 ami point. In Plethodon, where the secretion is restricted to 

 the tail though abundant there, autotomy occurs only as a last 

 desperate resource and but in one region. In Diemyctylus 

 where the secretion is copious and general over the body autot- 

 omy does not take place. 



Finally, passing from the region of fact and entering that of 

 hypothesis, it seems fair to conclude that we have in these three 

 species a case of adaptive correlation between autotomy and pro- 

 tective secretion. Batrachoseps appears to have, in its great 

 tail-shedding power, some compensation for its limited defensive 

 glands. Diemyctylus has no need of this, being sufficiently safe, 

 so far as one means of defense is concerned, in its own abundant 

 secretion. And, finally, it seems probable that when its tail 

 secretion fails the Plethodon, this species sheds that organ to 

 supplement the inadequacy of poison. 



