VOL. i.i Esterly. Poison Glands of Plethodon. 29 



Heidenhain ('98). Vollmer ('!):!) and Nicoglu ('93) . This 

 process consists in the growth into the old glands of a new and 

 smaller gland, which, however, is mucus in character, contrary 

 to the statements of Nicogln ('93), so that the poison glands 

 develop from the mucous to the poison variety. This has been 

 suggested but not definitely shown by Hover ('90) and Junius 

 ('98), and distinctly denied by all other investigators of the 

 regeneration of these glands. Under the histological structure 

 of the glands will be considered some new points in the muscu- 

 lature, especially as to the presence in the epidermis of an 

 apparatus for closing and opening the duct. The innervation of 

 the muscles and epithelium of the glands will also receive atten- 

 tion. 



This work was done under the direction of Professor C. A. 

 Kofoid, and my heartiest thanks are due him for very kind 

 assistance in every way and for criticism of results. 



MATERIAL AND METHODS. 



In order to obtain the best insight into the structure of the 

 glands of the tail, sections in three planes have been made of 

 that entire organ. The tissue was in all cases perfectly fresh 

 and was fixed in Zenker's fluid, which has been satisfactory in 

 all respects. Washing in 70.% iodine-alcohol followed the use of 

 the fixative. 



That bony tissue might not hinder the passage of sections in 

 any plane through the whole tail, the tissue was subsequently 

 decalcified in a 5% aqueous solution of nitric acid for from 

 twelve to twenty-four hours, followed by immersion in a 5% 

 aqueous solution of sodium sulphate for the same length of time, 

 and thorough washing in running water for from twenty-four to 

 forty-eight hours. 



Parafflue sections have alone been used, varying in thickness 

 from 3^ to 10 microns. The sections were fixed to the slide by 

 the water- albumen method, and in all cases where possible 

 staining was done on the slide. 



A considerable variety of stains has been employed. The 

 most successful have been Mallory's ('00) connective tissue stain 

 (acid fuchsiu, phospho-molybdic acid, anilin blue-orange G), 



