228 University of California Publications. [zoologv 



The poison i-'laiKls are in most rases much larger than those 

 of the mucous variety, and their enormous cells (Riesenzellen of 

 Leydig) completely fill the interior of the gland so that there is 

 no lumen. This character distinguishes these glands from the 

 others, which are provided with a low. cubical epithelium sur- 

 rounding a capacious lumen. (PI. XX. Fig. 2.) The mucous 

 secretion filling the lumen is very distinct from the heavily 

 granular contents of the cells of the poison glands. (PI. XXIII. 

 Fig. 31.) The two sorts of glands are further distinguished by 

 other features, chief of which is the staining reaction of the 

 mucous secretion (Nicoglu '93; Hover '90). These observers 

 used thionin as a specific staiu for mucus and found that the 

 small glands stain rose-red while the others are uncolored. 



The foregoing general facts have been determined chiefly upon 

 the Anura and the various European Salamanders, especially 

 Triton and Salamandra. But Plethodon oregonensis, a salaman- 

 der found about Berkeley, forms a particularly interesting object 

 for the study of the poison glands because of their unusual 

 development pn the tail of this animal. This seems to be a 

 protective character associated to some extent with the ability of 

 the animal to throw off its tail under stress of circumstances. It 

 has been shown by experiment that the secretion of the glands 

 of the tail is poisonous or obnoxious to certain animals, a char- 

 acter which probably belongs to the dorsal glands ( Hubbard, '03) , 

 which are very large and much more developed than elsewhere on 

 the body. In this respect Plethodon appears to resemble Triton 

 cristatus. (Capparelli '83.) However, the poison glands of 

 Plethodon are not confined to the dorsum of the tail; much 

 smaller ones are found on its ventral surface and also on 

 the trunk and head of the animal, intermingled with mucous 

 glands, which occur in all situations where the poison glands 

 are found. 



The principal question considered in the present paper con- 

 cerns the changes occurring in the formation of the secretion 

 and its expulsion from the glands. In Plethodon this involves 

 the death of the glands, as Seeck ('92), Nicoglu ('93), Vollmer 

 ('93) and others have shown for other Amphibia. The exhausted 

 glands are here renewed or replaced in the manner described by 



