vol.i.] Esterly— Poison Glands of Plethodon. 231 



It has been shown (Hubbard '03) that the swollen appear- 

 ance nf the tails of some animals is due to the increased 

 development of the poison glands posterior to the well-marked 

 constriction found just behind the cloaca in sucli e;ises. That 

 this is really true appears in the studj of a series of sections of 

 a swollen tail passing from the tip up to and including part of 

 the cloacal aperture. In the constriction the dorsal elands are 

 very small comparatively, and are here no larger on the back of 

 the tail than on the ventral side. But behind the constriction 

 their development is much greater, and one may trace the regular 

 increase in size as the series passes from the constriction back to 

 the enlarged portion of the tail. Everywhere in the tail, except 

 in the constriction at its base, the difference in size between the 

 glands on the dorsal and ventral surfaces is maintained. 



As is well known, the bodies of all the glands lie in a spongy 

 connective tissue, the middle layer of the corium, which in the 

 region of greatest development of the poison glands is increased 

 enormously in thickness (PI. XX, Fig. 1, m.c.l.) , being alone 

 from one-sixth to one-fourth or more of the dorsal -ventral dimen- 

 sion of the tail. ( Hubbard '03. ) The bottoms of the large glands 

 rest upon or come very close to the inner layer of the corium. 

 (PI. XX, Fig. 1, i.e. I.) 



The ducts of both mucous and poison glands pass through the 

 outer corium layer and the epidermis, the long axis of the gland 

 which passes through the duct and its mouth being perpendicular 

 to the surface at the point where the duct opens to the exterior. 



The histological structures found immediately surrounding 

 the ducts of the poison glands are in no essential points different 

 in Plethodon from those in other salamanders. The funnel cells 

 and their processes (PI. XX. Figs. 1 and 2. fl.c.) are present 

 as in Triton (Nicoglu '93) and in Salamandra (Ancel '02). The 

 membrane-like structure lining the duct belongs to a specialized 

 cell of the epidermis, corresponding to the "stoma cell" of Eberth. 

 As Nicoglu has shown, the mouths of the glands lie within these 

 cells, processes of which extend down in the ducts about as far 

 as the lower limit of the epidermis or a little farther. (PI. XXIII. 

 Fig. 27, p. fl.c.) The prolongations stain black in iron haema- 

 toxylin, reddish in Mallory's and yellow in Van Gieson's stain. 



