72 EVOLUTION AND DISEASE. 
been suggested by Mr. Eve, on very sood grounds, that 
the germs of teeth which have been suppressed in the 
evolution of our species may make themselves ob- 
noxious in an unexpected way. Teeth are formed in 
part by down-growths of epithelium lining the floor 
of the mouth; these cellular down-growths, known as 
enamel-organs, present distinctive features and are 
easily recognized by practised histologists. | The 
Fic. 34.—A follicular cyst developed in connection with an 
unerupted tooth of a Porcupine. The upper drawing 
shows the effects of the cyst on the jaw. 
mouth of man is occasionally occupied by tumours to 
which the name epithelial odontomes has been given ; 
the peculiar feature of these tumours is that they are 
composed of collections of cells in every way resembling 
the enamel-organ. The opinion receives considerable 
support from the fact that several carefully examined 
specimens of this peculiar form of tumour have occurred 
in cases where the number of teeth has been below the 
