VOL.!.] Vxtfi-li/. PoixoH Glands of Plethodon. . 243 



nuclei which in full glands lie at the bases of the cells, are in tliis 

 case in the inner parts of the cells, and are larger and clearer 

 and in a state of disintegration. In some places only outlines 

 or shadows of nuclei can lie seen. Often they became shrunken 

 and irregular in outline when the gland is emptied. The entire 

 appearance of emptied glands would lead to the conclusion that 

 their time of functional activity is at an end. 



The mucous glands, on the other hand, never reveal such 

 changes. It seems correct to say that the processes there are 

 like those in milk glands, where parts of the cell bodies ai-e 

 thrown oft' as secretion, while the remaining portions in time 

 repeat the same processes of secretion. Nussbaum ('82, p. 302; 

 speaks of the heads or inner portions of the mucous gland cells 

 of Salamander as discharged on stimulation. 



If it is true then, as it seems to be, that the poison glands are 

 changed bodily into the mass of secretion, we must look to some 

 source for their replacement, if the animal is to have their con- 

 tinued protection. Nussbaum's conclusions should be cited here 

 ('S2, p. 336) as bearing on the general topic of death of gland 

 cells through secretory activity, and their renewal. He says 

 secretion consists in the formation and elaboration of the mother- 

 substance of the secretion material, the changing of this in the 

 cells and in emptying the secretion when ready, out of the cells. 

 ''Wie alles Lebende aus uns unbekannten Ursachen abstirbt 

 und neuen Generationen Platz macht, so gehen auch nach einer 

 gewissen Zeit Driisenzellen zu Grunde und werden von leben- 

 skriiftigen Nachbarzellen ersetzt. Sterben aller Zellen gleich- 

 zeitig ab, so 1st die Driise vernichtet wie eine Protozoen Colouie. 

 Die Secretion mag wohl die Zelle abniitzen; die Zelle 

 wird altern. Der Ort der Secretion ist aber nicht gleich bedeu- 

 tend mit Zellentod; er ist eine energische Lebensthatigang." 



In this particular case of the skin glands of Amphibia, a 

 definite process of replacement goes on, occurring in Plethodon 

 in the way described for other salamanders by Nicoglu ('93), 

 Heidenhain ('93) and Vollmer ('93), and not as Junius ('98) 

 claims, by entirely new origin. The former observers find that 

 inside the old poison glands there lies a second smaller gland, 

 possessing a lumen. This small sac is to replace the older gland 



