234 University of California Publications. [ZOOLOGY 



Between the connective tissue layer and the gland epithelium 

 lies the layer of contractile or smooth muscle fibres. These were 

 first shown histologically by Hensche ('56), though before him 

 Ascherson ('40) had observed movements of the living glands. 

 Since this time there has been no doubt of the existence of 

 muscles in the walls of the poison glands (Coghill '99; Drasi-h 

 '89, '92, '94; Eberth '69; Eckhard '49; Englemann '72; Heid- 

 enhain '93 a, b; Leydig '76, a, b; Massie '94; Nicoglu '93; 

 Paulicki '85; Phisalix-Picot '00; Schultz '89; Seeck '91; Stieda 

 '65; Szczesny '67; Vollmer '93). As regards the smaller series 

 of glands the question seems to be open. The absence of con- 

 tractile fibres on them has been used as a character to separate 

 them from the large glands. The muscles of the large glands 

 are arranged in a single layer and have a general meridional 

 direction on the gland, converging toward the upper pole. The 

 fibres are usually simple but may be branched (PL XX, Fig. 7) ; 

 this occurs mostly on the lower part of the gland. Neither do 

 the muscles form a continuous sheet about the gland; the indi- 

 vidual fibres are separated by spaces of greater or less extent. 

 I have not been able to find with certainty muscles on glands 

 which are mucous in nature. 



The nuclei of the contractile cells, contrary to the description 

 of Nicoglu ('93, p. 437,) and such figures as his and those of 

 Vollmer ('93), lie in the upper region of the glands just outside 

 the uppermost gland cells, yet still well beneath the epidermis 

 (PL XX, Fig. 6; PL XXIII, Fig. 31, ,.). The first observer 

 mentioned has shown (his PL XXII, Fig. 12) the nuclei of the 

 muscle cells in various locations about the periphery of the glands; 

 but in Plethodon the nuclei have a constant position as described 

 and are found only there. In the region of the nuclei the muscle 

 fibres are considerably larger than elsewhere on the gland, as is 

 shown in PL XX, Fig. 8, m.f., or PL XXIII, Fig. 31, m.f., so that 

 the muscle, especially in longitudinal sections of the glands, seems 

 to bear a flask-shaped expansion. From this point it is possible 

 to trace a single fibre very nearh r to the base of the gland, and 

 also outward around the neck of the gland into the epidermis. 

 (PL XX, Fig. 6.) The connection of the muscles with the 

 epidermis has been reported by Nicogln ('93) and Heidenhain 



