MUCOUS MEMBRANE. 
intestinal villi,) and their sides tend to assume 
the direction of radii from a common centre. 
Hence they are sometimes even triangular in 
outline. Their opposite or free extremity is 
much thicker, often as thick as the part bulged 
by the nucleus, and near this extremity neigh- 
bouring particles are generally very intimately 
attached to one another, having often the ap- 
ted of being blended into a single mass. 
e best example of this is on the villi of the 
small intestine (fig. 280). The contiguous par- 
ticles, however, are fitted closely together in 
the greater portion of their length, and to effect 
this the bulging nuclei vary in the height at 
which they are placed. There can be no doubt, 
that, in certain situations at least, as will be 
afterwards shown, these particles are being con- 
tinually shed, and consequently are being per- 
petually renovated. But it is very difficult to 
ascertain their early condition and changes, and 
I am not aware of any satisfactory observations 
having been made for this end. From the 
great facility with which they become detached 
from the surface they invest, it is next to im- 
possible to examine them in situ on thin verti- 
Fig. 280. 
Villus of the intestinum ilium of the Dog, with the 
epithelium partially detached. 
@ a, solitary particles remaining attached ; 6, club- 
shaped extremity of the villus from which the 
epithelium has been detached; cc, epithelium 
at its base. Magnified 150 diameters. 
d, detached particles, shewing their close union, 
_ especially at the surface (at the letter); e, other 
detached particles, shewing their various shape, 
their nuclei and nucleoli. The letter is placed 
at their freeextremity. Magnified 350 diameters. 
Fig. 281. 
a, ciliated epithelial particle from the 
inner surface of the membrana tym- 
pani of the human subject ; 6, cili- 
ated epithelial particles from the 
bronchial mucous membrane of the 
human subject. All these shew the 
nuclei and nucleoli. Magnified 300 
diameters. 
491 
Epithelial particles from the cornu uteri of the Cow. 
The opposite cornu contained a foetus one inch and 
a half long. 
a, small particle, apparently in an early stage of 
development. ‘The nucleus is smaller than in the 
other specimens; b, another more advanced—the 
nucleus and surrounding substance are both 
larger, especially the latter, which presents a fine 
granular texture ; c, a particle made angular by 
pressure against others. It presents two nuclei, 
as though formed by fission; d, another of a dif- 
ferent shape; e, detached nucleus, showing its 
transparency and clear outline ; also two excen- 
tric dots, the nucleoli. Mugnified 300 diameters. 
cal sections. But there is no reason for sup- 
posing their mode of growth to be originally 
different from that of the scaly variety. Their 
nuclei probably appear first on the surface of 
the basement membrane, and around these a 
cell is developed (fig. 280, a). But this cell 
from its earliest period seems to contain an 
amorphous substance, which under high micro- 
scopic powers looks finely mottled, but not so 
definitely so as to allow of being called granu- 
lar. As the particle advances towards its full 
size, it loses its cell-membrane, and when com- 
plete is to be regarded rather as a solid mass of 
organic substance, surrounding a nucleus, than 
asacell. Here, then, is a striking difference 
between the scale and the prism: maturity 
being marked in the one by the disappearance 
of the substance of the cell; in the other, by 
that of the cell-membrane. 
Of the spheroidal variety (see figs. 273 to 
277).—In this the particles are of a rounded 
F ig 283. 
» Three epithelial particles from the 
Y human liver. 
a, nucleus ; 6, nucleolus ; ¢, fatty 
particle. 
Magnified 300 diameters, 
form, though generally somewhat flattened 
where they touch. They are always thick, 
from the substance they contain. It is this 
variety that constitutes the chief mass of the 
secreting glands, and hence it might not impro- 
perly be styled glandular. It corresponds with 
the prismatic variety, in its usually constitu- 
ting in the glands a single layer, and in the 
predominance, from the first, of its substance 
over its membrane. In the glands, indeed, the 
membrane can seldom be discerned at all, and 
the substance surrounding the nucleus, though 
more bulky, has the same finely mottled cha- 
racter already noticed in the prisms. In other 
situations the cell-membrane is persistent, but 
even then it never flattens into a scale. This 
variety presents in the different glands nume- 
rous modifications, which have not yet been 
studied with the accuracy they merit. It is 
