244 University of California PnblirutioHs. [ZOOLOGY 



and lies always between the musculature and epithelium of the 

 latter. Nicoglu ('93) iinds that the new glands possess "all the 

 epithelial parts of the old gland with the exception of the 

 "Schaltstiick." Whether this statement is to include also the 

 muscle fibres, he does not say; his figures show muscle cells 

 lying upon the ingrowing gland, but there is no reference to 

 prove that they belong to it rather than to the old gland. 

 However, Vollmer ('93) says that the new gland contains both 

 gland cells and smooth muscle fibres, which arise as does the 

 gland bud, from the Malpighian layer of the epidermis. 



The place of origin of the replacement glands is found by 

 Nicoglu ('93) and Heidenhain ('93r/) in the very small, flattened 

 cells immediately adjoining the Schaltstiick and lying inside the 

 gland. Vollmer ('93) on the other hand concludes that the 

 place of origin of the new gland "ist das Keimlager des Rete 

 Malpighi. Auch die von Heidenhain erwahnten unscheinbarer 

 Zellenelemente, denen er die Bildung der Driisenknospe zusch- 

 reibt stammen vom Rete Malpighi." There is no reason, he 

 says, why the new glands inside the old ones should not differ- 

 entiate as do the first glands in the course of their development. 



In Plethodon the method of renewal of the worn-out glands 

 is as these authors have described, but there is no evidence 

 showing the source of the replacement glands, and the subject 

 must be dismissed with the above references to the literature. 



But whatever the source of the new glands, there can be no 

 doubt that in every old gland without exception there is a small 

 sac or replacement gland. This is always found in those glands 

 which have not been discharged (PI. XXIII, Pig. 31), as well as 

 in those which have been and show the most extensive degen- 

 erative phenomena. In this respect Plethodon seems to differ 

 from Triton (Vollmer '93). This author states that the growth 

 of the new gland is initiated when the old glands are emptied. 

 Nicoglu ('93) mentions the fact that the old poison glands con- 

 tain the smaller sacs, but does not say definitely whether or not 

 the destructive processes must have set in before the the new 

 gland makes its appearance. But in Plethedon the presence of 

 the replacement gland is not dependent on the secretory processes 

 in the large glands. The former are present in the glands of an 



