56 Proceedings of Royal Society of Edinburgh. [sess. 
principal difference being that in Batoids the duct which leads 
from the gland proper to the rectum is short and comparatively 
wide, and opens into a posterior dilatation of the rectum, while in 
Selachians the duct is longer and narrower, and opens more 
directly into the rectum (Howes). The opening of the duct., 
which is usually guarded hy a fold of mucous membrane, is upon 
the dorsal wall of the rectum, about midway between the anus 
and the termination of the spiral valve. The gland is connected 
to the posterior abdominal wall by a fold of peritoneum, and is, 
according to Howes, supplied by the superior mesenteric artery. 
Its size varies in proportion to that of the animal, and in a skate 
of two feet in length from tip of snout to tip of tail may be about an 
inch in length; its colour is usually a reddish-brown. A longi- 
tudinal section shows that there is a central smooth- walled canal, 
irregular in calibre and giving off numerous short branches, sur- 
rounded by a firm glandular tissue, which is in its turn compassed 
by a whitish ring of fibrous tissue ; surrounding all is the coat of 
peritoneum. Along the lumen can be seen the mouths of severed 
vessels, and it contains some dirty-yellow secretion of a viscid 
consistence and a neutral reaction. Practically nothing more can 
be discovered by the unaided eye. 
Microscopic Appearances. 
Por the microscopic examination of the organ, specimens ob- 
tained in the freshest possible state were hardened in corrosive 
sublimate, formal in 8 per cent, solution, and in alcohol; and 
though good results were obtained by each method, it was 
noticed that the gland cells seemed to be best preserved by the 
alcohol ; there was, however, considerable shrinkage. The speci- 
mens were then embedded in the usual way in paraffin, cut by a 
rocking microtome, and stained either by hsematein and eosin, 
Ehrlich- Biondi triple stain, picro-carmin, or methyl-blue. Heiden- 
hain’s iron and bmmatoxylin method was also tried. 
The organ may be described as consisting of three regions : 
(1) An outer fibro-muscular layer covered by peritoneum. 
(2) A middle glandular layer. 
(3) A central region, consisting of ducts and blood-vessels 
arranged round a central lumen. 
