5 
changes occur, and much texture is probably produced and 
removed before the papilla attains its fully developed state. That 
passive substance called connective tissue which remains and 
occupies the intervals between the higher tissues, which 
possess active and special endowments, slowly accumulates, 
but undergoes condensation as the organ advances in age. 
Amongst this are a few nuclei which can no longer produce 
anything but indefinite “ connective tissue” of the same cha- 
racter. In PI. II, fig. 9, it would have been impossible, had 
the specimen been prepared in the usual manner, to have 
determined if the nuclei marked a, b were nuclei of the 
muscle concerned in producing muscle, or connective-tissue 
corpuscles concerned in the formation of connective tissue 
only. This question requires restudy from a new point of 
view. It is quite certain that many of the masses of germi- 
nal matter (nuclei) figured in all my drawings in connexion 
with nerves, vessels, muscles, and other tissues, would, if the 
specimens had been prepared in a different manner, so that 
their connexions were not so very distinctly seen, have been 
called “ CONNECTIVE-TISSUE CORPUSCLES.” 
The drawings accompanying my paper explain the rela- 
tion which I believe the essential structures entering into the 
formation of the papilla bear to the indefinite connective 
tissue in which they lie embedded. 
Epithelium. 
The so-called epithelium upon the summit of the papilla of 
the frog’s tongue (PI. I, fig. 1, a) differs from the epithelium 
attached to its sides {b), that covering the simple papillae (c), 
and that on the surface of the tongue generally, in many im- 
portant characters. As is w T ell known, it is not ciliated. The 
cells differ from the ciliated cells in several points. They are 
smaller than these. The nucleus is very large in proportion 
to the entire cell. The cells are not easily separated from one 
another, as is the case with the ciliated epithelium. These 
cells form a compact mass, the upper surface of which is con- 
vex. This is adherent by its lower surface to the summit of 
the papilla, and it is not detached without employing force. 
The cells do not separate one by one, as occurs with the ordi- 
nary epithelium, but the whole collection is usually detached 
entire, and then it is, I believe, torn away. 
Although some observers would assert that the two or three 
layers of cells represented in my drawings do not exist, but 
that the appearance is produced by the cells of a single layer 
being pushed over one another by pressure, I am convinced 
