VOL. i.] E.itcHij. Poison Glands of Plethodon. '24'} 



animal thirty-eight mm. long which are not filled with secretion. 



We have to deal then, in these cases, with the regeneration 

 of a gland by a gland. Individual cells are not broken down, 

 and then renewed by the growth of new cells as Schultz ('8!)) 

 maintains, and as seems to be implied by Calmels ('83), who 

 finds that the young gland cells are indifferent elements which 

 may develop into either poison or mucous cells, so that a gland 

 may be poisonous only in part. 



The question, however, as to whether a poison gland is 

 replaced only by a poison gland is still to be considered. May 

 not these be renewed by glands which to begin with are mucous 

 in character? That is, may not a specific poison secreting 

 epithelium be replaced through mucous cells, and gland by gland 

 instead of cell by cell ? These inquiries have been raised by 

 Xicoglu, and he says ('93, p. 425) that a mucous cell never goes 

 over into a poison cell, or vice versa, and Schultz ('89) also says 

 that mucous glands are always only mucous glands, and poison 

 glands only poison glands (p. 33), and therefrom we are to sup- 

 pose that the same is true of the individual cells, as he finds that 

 cells replace cells. 



Still the evidence gained by a study of the poison glands of 

 Plethodon indicates rather strongly that we have to deal with 

 <i production of poison glands from mucous glands fiilirely. 

 Nicoglu has already shown that in Triton a mucous gland 

 may sometimes replace a poison gland entirely, but he 

 very strongly opposes the idea that the function of such a gland 

 ever changes. He holds (p. 435) that the condition of mucus 

 within poison gland is a functional adaptation, because the 

 animal needs more mucous glands than are on hand. Everything 

 goes to show that in Plethodou, on the other hand, the occasional 

 method of regeneration described by Nicoglu is the only one. 

 The replacement glands already described stain blue without 

 exception in Mallory, which has been shown to be a mucous stain. 

 The contrast between the blue of the mucus and the red of the 

 granular secretion is very sharp (PI. XXIII, Fig. 31). The 

 mucous reactions described for Van Gieson, orcein and mucicar- 

 inine, are shown invariably in the replacement glands as in the 

 mucous glands outside, and the correspondence of the replacement 



