VOL. i.] Esterly. Poison Glands of Plethodon. 237 



well in cross sections of the gland ducts in the epidermis where 

 the cut ends of the muscles arc seen dose beside the funnel cell 

 (PI. XXIII, Figs. 28, 20, prol. tii.f.). In good longitudinal 

 sections of the ducts the muscles (PI. XXIII, Fig. 27, prol. 

 m.f.) are seen to end between the older replacement cells which 

 are already elongating into their typical form (same, rep. r.). 

 Xi. -no-lii ('():!) represents the endings as between the cells, but 

 Aucel ('02) seems to consider them as special parts of cells. At 

 any rate he has shown (Fig. 22) the fibrils as within cells in the 

 epidermis. I have not been able to find such structures as he 

 shows; there can be hardly any doubt that the prolongations of 

 the gland muscles into the epidermis end between the replace- 

 ment cells. Nicoglu and Heidenhain ('93) and Ancel ('02) have 

 remarked upon the existence of intercellular bridges between the 

 muscle cell on the one hand and ectodermal epithelial cells on the 

 other, as Nicoglu says (p. 440), "von ga7iz ahulicher Art wie 

 zwischen den Oberhautzellen selbst." 



I have not found the intercellular bridges in Plethodon 

 between epithelial and muscle cells, but all the facts concerning 

 the connection of muscle and epidermal cells have been taken as 

 evidence of the ectodermal origin of the muscles of skin glands. 

 This has been so often commented upon that it is useless to more 

 than call attention to it here. The evidence gained from a study 

 of the development of the glands shows that the muscle fibres 

 come from the Malpighian layer of the epidermis (Ancel '02; 

 Vollmer '93; Junius '98). This, added to the facts already 

 cited, and coupled with the observations of many investigators 

 (Engelmann '72; Seeck'91; Heidenhain '93; Nicoglu '93) seems 

 fairly conclusive that the muscles of the dermal glands are of 

 ectodermal origin: (Compare also in case of sweat glands, 

 v. Kolliker '89; Handbuch des Gewebelehre des Menschen, pp. 

 138 and 258). 



The existence of a sphincter or constrictor muscle for the 

 glands has been claimed by Schultz ('89), who described a band 

 of muscle fibres running around the neck of the gland beneath 

 the meridional layer. This observation has been disproved by 

 Drasch ('94) and Nicoglu ('93), and I have been unable to find 

 such a structure in Plethodou. And there is no evidence of the 



