vol. l.] Esterly.— Poison Glands of Plethodon. 245 



animal thirty-eight mm. long which are riot filled with secretion. 



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

 nf a gland by a gland. Individual cells are nol broken down, 

 and then renewed by the growth of new cells as Schultz ('89) 

 maintains, and as semis to lie implied by Calmels ('83), who 

 finds that the yonng gland cells are indifferent elements which 

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

 may lie poisonous only in part. 



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

 replaced only by a poison eland is still to lie considered. Ma\ 

 not these lie renewed bj glands which to begin with are mucous 

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

 epithelium lie replaced through mucous cells, and eland by gland 

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

 Nicoglu, and he says ('93, p. 42~>) that a mucous eel] never goes 

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

 that mucous elands are always only mucous elands, and poison 

 glands only poison elands (p. :;:;). 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 elands of 

 Plethodon indicates rather strongly that we have to deal with 

 a production of poison glands from mucous glands entirely. 

 Nicoglu has already shown that in Triton a mucous gland 

 may sometimes replace a poison eland entirely, but he 

 \er> stronglj opposes the idea that the function of such a gland 

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

 within poison eland is a functional adaptation, because the 

 animal needs more mucous elands than are on hand. Everything 

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

 method of regeneration described by Nicoglu is the only one. 

 The replacement glands alreadj described stain blue without 

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

 The contrast between the bine 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- 

 liiine. are shown invariably in the replacement glands as in the 

 mucous glands outside, and the correspondence of the replacement 



