250 University of California l*ubrH-<iii<>ns. [ZOOLOGY 



expressed, that the glands which are to replace the worn-out 

 poison glands are originally mucus in character. 



There is no reason to believe, however, that the replacement 

 glands are functionless during the life of the poison glands in 

 which they lie. Even the smallest replacement glands have 

 distinct ducts and epithelium, and in some cases it is absolutely 

 certain that they have elaborated a secretion similar in every 

 respect to that of the mucous glands. 



It is very probable that under all ordinary conditions the small 

 glands in the large ones secrete mucus, and in thi> sense art- 

 adaptations; not because the animal through some unusual 

 external conditions has come to need more mucous ghinds as 

 Nicoglu ('93) says, but rather because under normal environ- 

 ment there is always need of more mucus than can be secreted 

 by the glands outside the poison glands, especially when the 

 latter are so closely crowded together as on the back of the tail 

 in Plethodon. And much evidence goes to show that under 

 stress of necessity such mucus secreting glands become by 

 replacement the more highly specialized poison glands and take 

 on a particular function, that of forming a substance protecting 

 the animal from its enemies (Hubbard '03.) 



The nerve supply of the skin of Amphibia has been a favorite 

 subject of study for many years. Most investigators have limited 

 themselves to the terminations in the sense organs of the skin 

 and in or on the ordinary epidermal cells (Pfltzner '82; Cauini 

 '83; Preukel '86; Massie '94; Herrick and Coghill '98; Coghill 

 '99) . The innervation of the glands has received less attention. 



Eckhard ('49) first showed that the glands could be emptied 

 by stimulating the anterior roots of the cerebro-spinal nerves, 

 but did not consider the structure of the nerve endings. Eberth 

 ('69) found that there is a network of very fine fibres close upon 

 the glands; Englemann ('72) came to the same conclusion and 

 showed farther that from the nerves about the gland fine twigs 

 are given off to the contractile cells. Openschowski ('82) 

 describes a network of nerves surrounding the glands, as well 

 as an iutracellular net; but from his figures it is hard to believe 

 that the structures he shows are nerves. Drasch ('89) also experi- 

 mentally proved the efficacy of nerve stimulation iu obtaining 



