158 University of California Publications. [zoology. 



Beyond the questions of the structure and development of the 

 glands, of their differentiation into such types as serous aud 

 mucous, of the chemical nature aud physiological effects of the 

 secret ion, lies the fundemental problem of the role of the glands 

 in the economy of the animals. This last problem has been much 

 less studied than the others. 



Some doubt is now being cast on the theories of protection in 

 the animal kingdom that have been most in favor for half a 

 century. Many structures and products of the organism hitherto 

 regarded as sufficiently explained when they have been shown to 

 be defensive are seen to owe their existence to more direct and 

 simpler causes, as, for example, physiological activity, the effects 

 of climate and other environmental influences, etc., and conse- 

 quently if protective at all are often so only secondarily. 



The study, the results of which are embodied in these notes. 

 at first aimed merely at finding the nature of the enlarged 

 condition of the tail in one species of salamander, Plethodon 

 oregonensis. As the work advanced, however, its scope broadened 

 until it touched upon the general problem of animal protection, 

 the particular aspect of the problem chiefly involved being that 

 of the correlation of protective devices. 



The salamanders upon which observations have been made are 

 Plethodon oregonensis Girard, Diemyctylus torosus Eseh., and 

 Batrachoseps attenuatus Esch. A fourth species, A utodax hit/til/rls 

 Hallow., occurs commonly at Berkeley, but does not enter into 

 these notes because of the difficulty of obtaining specimens at the 

 time the work was being done. Batrachoseps aud Diemyctylus 

 are very abundant, the former living under stones, old boards 

 and rotting logs in damp, shady places, while the latter is 

 found almost everywhere, but is especially given to congregating 

 in the water of reservoirs and in quieter places in streams. 

 Batrachoseps has a habit of burrowing in the soil, almost like an 

 earthworm. Plethodon, though uot so abundant as the other 

 two species, is not uncommon. Like Batrachoseps it is found 

 under rocks, logs aud old boards, in moist, shady places. Neither 

 of the last two species appears ever to enter the water. 



Diemyctylus is diurnal in its habits, while Plethodon is noc- 

 turnal. I have never found a specimen of the latter abroad in 



