522 JOHN BERRY HAYCRAFT AND BE. W. GCARLIER. 
nective-tissue corpuscle. If Kolliker is right, the osteoclast 
may divide and form osteoblasts where absorptive processes 
are being replaced by formative ones, and the osteoblast may 
become an osteoclast where the reverse process is taking place ; 
and Klein has described the replacement—during deyvelop- 
ment—of ciliated by stratified squamous epithelium, on the 
posterior or upper part of the soft palate, a case identical with 
the one we have noted. 
In most of these cases the cause of the change is unknown; it 
is possibly environmental, but one can say little more. In the 
case of the transformation of the ciliated into the stratified 
squamous epithelium the environmental cause is very obvious. 
The exact way in which friction acts, when it produces the 
changes we have described, it is impossible to say. 
We may, perhaps, look upon all stratified squamous surfaces 
as having been developed at one time or another by the action 
of friction, and we may speak of them, in this sense, as fric- 
tional epithelia. 
We have much pleasure in expressing our thanks to Mr. 
Gustav Mann for his kindness in making the drawings from 
which the figures in the plate were lithographed. 
EXPLANATION OF THE LOWER PART OF 
PLATE XXXIII, 
Illustrating Dr. Haycraft’s note on the ‘Transformation of 
Ciliated Epithelium.” 
Hie. 5.—Transverse section through the posterior third of the trachea of an 
adult cat. 4. Ciliated cells lining general cavity. 2. Situation where 
stratified squamous cells are found. C. Marks bottom of groove; the epi- 
thelium between C@ aud B is transitional in character. D. Cells are columnar, 
but without cilia. #. Cartilage. #. Trachealis muscle. 
Fic. 6.—Transverse section through the posterior third of the trachea of a 
kitten two weeks old. #. Cartilage. #. Trachealis muscle. H. Fold of 
mucous membrane into which the cartilage is growing. 
Fic. 7.—EHpithelium from the general surface of the treachea. 
Fie. 8.—Epithelium from between B and C. 
Fre. 9.—Stratified squamous epithelium found at B, 
