INTEGUMENT OF NECTURUS MACULOSUS 551 
into these positions by the pressure developed by the contracting 
muscles. In many cases, therefore, contraction appears to result 
in the almost complete obliteration of the gland lumen and the 
removal of a large proportion of the nuclei of the old secretory 
epithelium. However, there are always a few nuclei left within 
the gland sae and they are usually elongated on the side toward 
the muscular layer (fig. 20), indicating that originally they had 
been attached to this region and were pulled into the form they 
now assume as a result of the contraction of the muscular wall 
and its subsequent withdrawal due to the elasticity of the dermis. 
Emptied glands; although their volume is greatly decreased, 
always retain their spherical or ovoid form. ‘They never present 
the collapsed appearance described by Drasch (’94), Nirenstein 
(08), Muhse (’09), Shipley and Wislocki (’15), and others. The 
muscle layer is always prominent and the intercalary region is 
drawn down and elongated. Often the epidermis above suffers 
considerable distortion and in many cases epidermal cells are 
torn away, due either to the force of the escaping secretion or to 
the incomplete development of the duct. 
In undischarged glands the muscle fibers are very thin and 
greatly elongated, and can be distinguished with certainty only 
under the higher powers of the microscope. Their nuclei in 
perpendicular sections also appear long and thin. In the con- 
tracted condition, the fibers are easily seen, being greatly thick- 
ened and shortened. Their nuclei, too, undergo corresponding 
changes in form. In material killed and fixed immediately after 
the expulsion of secretion the contracted muscles show little 
fibrillar structure and stain intensely in eosin. In tissue pre- 
pared twenty-four to forty-eight hours after the emptying of the 
glands, myofibrillae are easily seen and the muscle fibers do not 
take the eosin so readily. 
In the poison glands of Salamandra maculosa, Drasch (’94) 
described cross-striations on the contracted fibers and regarded 
them as being due to wrinkling of the membrana propria of the 
gland, and not to any change in the surface of the fibers them- 
selves. Also in Necturus cross-striations were noted and are 
clearly shown in tangential sections of the gland in which the 
JOURNAL OF MORPHOLOGY VOL. 34, NO. 3 
