266 
ME. CHAELES S. TOMES ON THE 
The presence of an enamel-organ in the foetal narwal has been described by Professor 
Turner (Journal of Anatomy and Physiology, 1873) ; its occurrence in a foetal 
armadillo by myself (Quart. Journ. of Micros. Science, 1874); while in the present 
paper instances of its occurrence where little or no enamel is formed are noted. 
4. So far as my researches go, a stellate reticulum, constituting a large bulk of the 
enamel-organ, is a structure confined to the Mammalia f (it is absent in the armadillo, 
and I should infer, from Mr. Turner’s description, in the narwal). 
5. As laid down by Professor Huxley and Professor Kolliker, the dentine-papilla is 
beyond all question a dermal structure, the enamel-organ an epithelial or epidermic 
structure. 
As I believe it can be shown that the enamel is formed by an actual conversion of 
the cells of the enamel-organ, this makes the dentine dermal, and the enamel epidermic 
structures. 
6. In Teleostei the new enamel-germs are formed directly from the oral epithelium^ 
and are new formations arising quite independently of any portion of the tooth-germs 
of the teeth which have preceded them. In mammals and reptiles, and in some, at all 
events, of the Batrachia, new tooth-germs are derived from portions of their predecessors. 
7. In all animals examined the phenomena are very uniform : a process dips in from 
the oral epithelium, often to a great depth ; the end of the process becomes transformed 
into an enamel-organ coincidently with the formation of a dentine-papilla beneath it. 
The differences lie rather in such minor details as the extent to which a capsule is 
developed ; and no such generalization as that the teeth of fish in their development 
represent only an earlier stage of the development of the teeth of Mammalia can be drawn. 
Description op the Plate. 
PLATE 31*. 
Fig. 1. Transverse section of the lower jaw of a young dogfish, Scyllium canicula. 
To the right is seen the thecal protecting fold of mucous membrane, slightly 
displaced. Between this and the jaw is seen the chain of enamel- organs, 
which, if the parts were exactly in situ , would solidly fill up the whole inter- 
space. The epithelium, where it passes across from the jaw to the thecal 
fold, between the third and fourth tooth, is torn across. 
a. Oral epithelium. 
b. Neck of enamel-organ connecting it with oral epithelium. 
c. Special “ bone of attachment.” 
t It is also to be found in the poison-canal of the partly calcified tooth-germs of poisonous snakes, as I 
have described and figured in a paper upon tbe development of poison-fangs, in course of publication in the 
Philosophical Transactions. 
