vol. i.i Esterly. — Poison Glands of Plethodon. 235 



('93 b), and the arrangement in Plethodon is a similar one 

 except as regards the presence of the "Schaltstiiek" cells described 

 by them. In Plethodon the "Schaltstiiek" is not demonstrably 

 present except in one or two questionable cases in all my prepa- 

 rations, and Vollmer ('93) found that it is very often absent 

 even in Triton. There can be no doubt, however, that the 

 muscles send processes into the epidermis. This is especially 

 well shown in longitudinal and cross sections of the ducts. 



The statement that the muscle nuclei of the poison glands in 

 Plethodon lie only in the necks of the glands, instead of generally 

 distributed about the periphery as held for other animals, may 

 be supported by several facts. In the first place, longitudinal 

 sections of the glands through the duct and mouth show two 

 nuclei, one at each side of the gland where the sac begins to pass 

 over into the duct. In sections of the same plane which pass a 

 little to one side of the duet (PI. XXI, Fig. 10, inf., mn.) may 

 be seen in some cases the obliquely cut ends of as many as seven 

 muscle cells each with its nucleus in situ, and occupying exactly 

 the position relatively of the two lateral nuclei which are shown 

 in the median section. There can be no doubt of their structure. 



Cross sections of glands and ducts are also very instructive 

 on this point. In such, especially if stained in Van Gieson 

 (PI. XX, Fig. 12), there are shown in many cases the light yellow 

 muscle fibers between the gland cells and the connective tissue, 

 when the plane of the section passes more deeply through the 

 gland than the position of the nuclei of the muscles. But when 

 the eland is cut across at the level of the nuclei, the evidence 

 gained from longitudinal sections is even more strikingly upheld. 

 In such cross sections can be seen as many as twelve or fourteen 

 muscle fibres stained light yellow (in Van Gieson), and in very 

 sharp contrast to them the brown or black nuclei. And in this 

 region the section of the muscle is larger than it is deeper in the 

 gland: this corresponds to the flask-shaped enlargement seen in 

 median longitudinal section (PI. XX, Fig. 8, mf.). If a series 

 of frontal or cross sections of the tail is studied, it will be found 

 that while the muscles themselves can be traced until the bottom 

 of the gland is reached, nuclei never appear again which are 

 unmistakably those of the muscle fibres. The only place in 



