448 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
There are two series of spaces seen in sections 
through the gland—the lumen or gland cavity lined by 
epithelium with all its diverticula, and the blood spaces 
bounded by the connective tissue in which they he 
(figs. 42 and 45, Aen. v.) and containing scattered 
corpuscles, so that the blood is only separated from the 
glandular epithelium by a thin layer of connective tissue. 
The glandular epithelium is composed of cells which 
are about three times as tall as their width. The cells do 
not contain much stainable protoplasmic contents, and 
high magnification shows that they are much vacuolated 
with the protoplasm situated near to the cell bases, 
towards which end the nucleus is also to be found. The 
large vacuole occupying most of the cells is filled by a 
refractive colourless or slightly brown crystalline body, 
which is a concretion of excrete matter. The free 
surfaces of the cells facing the lumen of the gland bear 
delicate processes almost exactiy like cilia, so that in 
some places it is very difficult to detect any difference. 
They are irregular in distribution, sometimes quite 
abundant, and have also a beaded appearance which makes 
them a little unlike cilia—which, moreover, have not 
been found on the cells of the renal organ of Lamelli- 
branchs It is unusual for excretory cells (loaded with 
excrete matter in many cases) to have cilia, and IT am 
inclined to think, therefore, that this very cilia-like 
appearance is due to an excretion which takes place in a 
fibrous manner. There are generally present in the 
lumen of the organ masses which look as if they contained 
these cilia-like processes. In the figure (fig. 52) these 
are too much like cilia, and are rather too regularly 
disposed. In addition to these processes there are always 
to be found cells in the act of extrusion, so that by actual 
dehiscence of the cells the excretion is thrown into the 
