46 CHARLES S. TOMES. 



tions of the future dentine germ, the first thing of which he 

 can be positive is the enamel germ, which at this early period 

 is far in advance of the other component parts of the tooth 

 in respect of its development. In thinking over the in- 

 creased importance from a homological point of view, which 

 is given to the enamel organ by its very early appearance and 

 its entire independence of the dentine and cemental germ in 

 its origin, it occurred to me that it would be exceedingly 

 interesting and instructive, to examine the tooth germ 

 of a mammal whose teeth are not coated with enamel ; 

 and I hasten to acknowledge the kindness of Professor 

 Agassiz in America, of Professors Rolleston and Westwood 

 at Oxford, and of Professor Flower at the Royal College of 

 Surgeons, for placing all the material which they possessed 

 at my disposal. 



The difficulty of the inquiry Avas very greatly enhanced 

 by the condition of the specimens, Avhich had all been kept 

 in methylated spirit of varying strength, and it was extremely 

 troublesome to make sufficiently thin sections, as the tissues 

 were very friable. The best results were obtained by placing 

 them in absolute alcohol, whence they were transferred to 

 strong glycerine, and then imbedded and cut in the usual 

 way. 



In order to make my description more intelligible I have 

 placed side by side with the figures of the dental germs of 

 the armadillos a drawing of a section through the lower 

 jaw of a calf (fig. 1), to some few points in which I will 

 draw attention before comparing and contrasting them with 

 one another. 



The enamel organ (c) in this figure forms a cap, em- 

 bracing the upper part and sides of the dentine germ {b) ; 

 it is seen to be still connected with the epithelium (deep 

 layer) of the mouth by a thin dark line, which, under 

 favorable conditions of lighting, &c., may be seen to consist 

 of a double row of cells. AVhere this merges into the enamel 

 organ these two rows of cells separate and pass round the 

 periphery of the enamel organ, forming what is known as 

 the " external epithelium of the enamel organ ; " near to the 

 base of the dentine germ this layer of epithelium is reflected 

 upon it, and forms a complete investment to its surface, in 

 ■which situation it is termed the " internal epithelium of the 

 enamel organ." 



But in the calf these external and internal epithelia are 

 widely separated and form but a small proportion of the whole 

 bulk of the enamel organ, the intermediate space being 

 occupied during the formation of the enamel by a stellate 



