374 THE SKIN AND THE SENSE-ORGANS. 



short distance (o'oi 5-0*022 mm.) from the upper or superficial 

 pole each fibre has an ellipsoid thickening-, composed of granular 

 protoplasm, and containing- a clear oval nucleus. 



The inner coat is composed of a single layer of epithelium, placed 

 directly on the muscular coat. The epithelium has a thickness of 

 about o*oi-o*02 mm. ; it is, however, usually thicker towards the 

 base than towards the duct. The boundaries between the cells are 

 very indistinct, and so give the epithelium the appearance of a con- 

 tinuous layer of protoplasm. The glandular epithelium is not 

 directly continuous with the epithelium of the duct. 



The shape of the cells depends upon their physiological condition. 

 In a state of semi-contraction of the gland, the cells are cubical, and 

 their free borders pushed into the lumen in a slight convexity; 

 when the gland is fully distended the cells are two or three times as 

 broad as deep ; in a fully contracted gland the cells are conical or 

 cylindrical. In the first-mentioned condition their diameter varies 

 from 0'Oo6-0'Oi8 mm. The larg-er g-Iands are estimated to possess 

 about 150 cells, the smaller only thirty to forty (Engelmann). 



The cells appear to have no cell-wall, certainly they possess none 

 on their free surfaces. Their protoplasm distends very freely on 

 the addition of water. As a rule some cells are much more gran- 

 ular than others of the same gland ; each cell has a rounded oval, 

 clear nucleus, and vacuoles are frequently met with. 



The lumen of the gland contains a colourless, transparent, watery 

 fluid, which contains mucous material. 



The ducts of the glands are thick-walled cylinders, circular in 

 section. Their diameter varies from ©•02-o-o5 mm., their length is 

 equal to the depth of the superimposed epidermis. The wall of the 

 duct is lined with two or three concentric layers of highly refrac- 

 tive, nucleated cells. The cells are arranged parallel to the length 

 of the duet : in transverse section they are sickle-shaped or semi- 

 lunar. In the upper third or fourth of the duct the inner wall is 

 lined with a cuticle, very résistent to the action of acids or alkalies : 

 it is thrown off with the skin in the process of casting. In the horny 

 layer of the epidermis this cuticle is partially closed by a stoma- 

 cell (Eberth), (Fig. 230), which possesses a tri-radiate opening. 



The glands correspond with the ' non-contractile glands ' of Hensche, the ' dark 

 and bright glands ' of Stieda, the ' glandule niezzane, piccole e piccolissime (ad epitelio 

 pavimentoso) ' of Ciaccio, and the ' small, dark, and medium-sized, bright glands ' of 

 Eberth. 



e. The peculiarities oî the skin of the supplemental toe and 



