238 University of California Publications. [zoolo«y 



epithelial plug of Drasch ('94) for restraining the contents of 

 the gland under pressure. Phisalix-Picot ('00) mentions (pp. 

 44-45) an orbicular muscle, but gives no description or drawing 

 of it. so that her meaning is obscure. Dilator muscles for the 

 ducts or mouths of the glands have never been described. 



However, both dilator and constrictor muscles occur about 

 the mouths of the poison glands of Plethodon. These are best 

 shown in sections of the epidermis parallel to the surface, stained 

 in Mallory's connective tissue stain, which are, of course, also 

 cross sections of the ducts. All three sets of gland muscles may 

 very often be seen in one such section (PI. XXIII, Fig. 30, con. 

 in.. dil. in., m.f.; Figs. 28, 29 also). In these eases it will be seen 

 that the duct (1.<1.) in the epidermis is oval in cross section, and 

 that at each end of the oval is a triangular mass of fibres, stain- 

 ing red in Mallory, as do the muscles on the body of the gland. 

 The fibres converge toward the duct and insert upon the replace- 

 ment cells nearest the funnel in such a way that by contracting 

 they will bring the lips of the duct together and so close or 

 greatly diminish its lumen (PI. XXI, Fig. 16). The con- 

 strictor fibres are differentiations of the cell whose large nucleus 

 (PI. XXI, Figs. 14, 16; PI. XXII, Fig. 28, nuc. ep.m.c.) , 

 stands at the ends of the elliptical opening of the duct. The 

 fibres lie within this cell as can be especially well seen in longi- 

 tudinal sections of the glands which do not pass through the 

 duct. Here it appears that the cell of which the constrictor 

 fibres are a part, together with its nucleus, lies in the deepest 

 layer of the epidermis immediately upon the outer layer of the 

 corium. This cell seen in surface view is equal in extent to 

 several of the neighboring epidermal cells, but in cross section 

 it is very much flattened (PI. XXI. Fig. 13). Ancel ('02) 

 has figured such a cell, but gives no clue as to its function. 



The dilator fibres belong to the same cell of which the con- 

 strictors form a part, and are at a slightly lower level seemingly 

 than the latter. The action of the dilator is two fold. Some 

 fibres pass around the ends of the oval opening of the duct 

 (PI. XXIII, Fig. 28, dil. m.; PI. XXI, Fig. 14) and when they 

 shorten they tend to separate the lips of the lumen more widely. 

 by pressing at the ends of the ellipse. This is evident when it 



