vol. i.] Esterly .—Poison Glands of Plethodon. 249 



Eere there is very frequently a distinct blue tinge to the granular 

 secretion. This maj possibly be because the metamorphosis 

 from "a mucus-like substance to the poison secretion" is not 

 entirely completed. At any rate one is impressed with the like- 

 lihood thai there is mucous material in the poison glands outside 

 of that contained in the replacement glands. 



In the discussion of the replacement of the poison glands by 

 those of the mucus variety, it has been shown that every large 

 "•land lias within it the fundament of a new gland which to all 

 stains for mucus except tliionin gives the mucous reaction, and 

 which is also the exact counterpart of the small glands having 

 the mucous secretion. The fact that only in poison glands of 

 smaller size are found evidences thai they arc entirely replaced 

 by mucous glands, maj be explained on the ground that there the 

 amount of granular secretion is not sufficient to mechanically 

 hinder the growth of the new replacement gland. The actual 

 transition stages from mucous to granular secretion have not been 

 observed in my material. 



If we make the assumption in view of these facts that the 

 elands of mucous character in the poison glands develop only into 

 mucous glands on the death of the latter, we arc forced to one of 

 two conclusions: cither that the small glands outside the large 

 ones, especially in Plethodon on the dorsal surface of the tail, 

 become the poison glands, or, on the other hand, that when the 

 latter are once destroyed there is no return to such struct- 

 ure except by developing anew according to the embryonic 

 type. 



The latter process is going on continually in large as well as 

 in small animals, as can be readily seen by inspection of sections. 

 But it seems that the fundaments are all alike to begin with 

 (Anccl '()"_!); as this author says, the solid gland buds in which 

 a cavity is formed do not undergo further important morpho- 

 logical transformations, and constitute the mucous glands. Those 

 which remain solid, however, continue their development in other 

 ways and form the poison elands (p. 2G'J) . It seems to me that 

 this is equivalent to saying that in embryological development 

 the poison glands pass through a mucous stage to reach their final 

 form and character. It certainly lends evidence to the view 



