248 University of California Publications. [ZOOLOGY 



diminution in size of the lumen of the gland, together with the 

 vesicular structure of the cells, would lead one to think that they 

 are in the way of becoming granule or poison cells. But what- 

 ever the interpretation put upon this appearance, and to what- 

 ever source it is due, it must be admitted that the fundaments in 

 the old poison glands have undergone the same processes and 

 their histological characters are now exactly similar to those of 

 the mucous glands. 



Further evidence that the glands are originally all of the 

 same character may be gained from the literature. Ancel ('02), 

 who has followed very closely the development of the skin glands 

 in salamander, considers that the large glands represent organs 

 more completely differentiated than the small glands toward a 

 special functional adaptation, though both in early development 

 are absolutely alike (pp. 269, 283.) Jiuiius ('98) believes 

 that there is but one kind of gland in the skin of the frog and 

 probably of all Amphibia, and that the various glands of the 

 authors are young and old forms or developing stages of them. 

 He says further that in the frog he has not seen the regeneration 

 described by Vollmer and Nicoglu, and declares that atrophied 

 glands are replaced by wholly new ones developed by down- 

 growths of epiderm cells into the cutis. According to him, 

 small glands represent young stages of large ones, and the for- 

 mer are equivalent to the non-contractile or mucous glands, while 

 the latter are the dark, contractile, granule or poison glands. 



Again, Hoyer ('90, p. 354) finds that in some poison glands 

 of the salamander single cells or groups of cells lying between 

 the non-staining large granular cells take on a red-violet color 

 in thionin (which he employs as a specific mucous stain). He 

 makes the suggestion merely: "Moglicher Weise deutet dieses 

 eigenthiimliche Verhalten auf eine genetische Beziehung der in 

 den Driisenzellen enthaltenen mueinahnlichen Substanz zu dem 

 giftige Secrete." And finally, the observation of Phisalix-Picot 

 ('00) that the secretion of the mucous glands of the Salamander 

 is poison, seems to me to bear along this line of a correlation 

 between the so-called mucous glands and the poison glands. 



Evidence in this direction also, further than that already 

 advanced seems to be indicated in the poison glands of Plethodon. 



