THE SALIVARY AND OTHER GLANDS OF THE COLUBRID^. 519 



labial gland consists of two isolated portions ; and in all the 

 Colubridse the lining epithelium of the ducts, even to within a 

 very short distance of their orifices, consists of secretory cells 

 similar to those o£ the alveoli. The latter are large and some- 

 what irregular, and the lumen varies in size considerably in the 

 different groups of snakes. lu the Proteroglyphous Colubridae 

 the lumen is large and the epithelium is but one layer of cells 

 thick. In the Aglyphous and Opisthoglyphous forms, however, 

 the epithelium consists of several layers of cells and the lumen 

 of the gland is correspondingly smaller. A drawing is given in 

 fig. 9 (PI. 35) of the resting state of the gland in a species of 

 Heterodon, and in it the small size of the lumen as compared with 

 the size of the alveolus is most clearly seen. A few alveoli from 

 the superior labial gland of an Opisthoglyphous snake, Dipsas 

 ceylonensis, killed during active secretion, are represeuted in 

 fig. 10. A consideration of these two figures affords distiuct 

 evidence that the mucus-secreting cells are for the most part 

 disorganized and discharged during secretion; this could only be 

 inferred from fig. 9, as those cells not adjacent to the lumen of 

 the alveoli would be unable to discharge their secretory product 

 without the disorgauization of those that intervene, but in 

 fig. 10 this disintegration of the mucus-secreting cells is 

 clearly shown. The preparations leave no doubt in my mind 

 that these cells are replaced by others which arise by pro- 

 liferation of certain subepithelioid cells {p-c. fig. 10) located 

 towards the exterior of the alveoli and more or less flattened 

 against the basement-membrane — cells which are evidently the 

 homologues of those known to the human anatomist as the 

 'marginal cells,' constituting the crescents of Q-ianuzzi or the 

 demilunes of Seidenhain *. 



It has been stated by certain physiologists that broken-down 

 mucus-secreting cells rarely, if ever, occur, and that a supposition 

 that any considerable breaking down takes place is quite unwar- 

 ranted. These statements do not apply to the mucous glands 

 of the Ophidia, since in many of these animals the breaking down of 

 the cells is certainly very extensive. One cannot but be convinced 



* These cells have been recently stated by Krause ("Beitrage zur Histologie 

 der Speicheldriisen," Archiv f. mikr. Anat., Bd. xlix. 1897) to be sometimes 

 albumen-forming in the submaxillary glands of vertebrates. 



37* 



