TOOTH DEVELOPMENT DASYPUS NOVEMCINCTUS 657 



that the enamel pulp has disappeared in the 82 mm. embryo, 

 leaving a compact layer of cells representing the outer and inner 

 enamel epithelium and the stratum intermedium. Thus at first 

 the enamel organ is composed of an outer enamel epithelium 

 stellate reticulum, stratum intermedium, and inner enamel epi- 

 thelium. The ameloblasts are always unusually short, but, as 

 has been pointed out by Tomes, there is a great variation in the 

 length of ameloblasts; they are longest "when enamel formation 

 is most active and a material thickness of enamel is to be formed" 

 (Tomes '14, p. 169). In D. novem. as shown in figures 4, 5 and 

 7, an exceedingly thin layer of enamel is always deposited. 

 The enamel organ disappears early, but this is due to the fact 

 that its function is performed early, and so there is no necessity 

 for its longer persistence. I have never been able to demonstrate 

 the presence of stellate reticulum over any part of a tooth pos- 

 sessing a visible deposit of enamel. The stellate reticulum, then, 

 is the first part of the enamel organ to disappear, the outer and 

 inner epithelia finally coming into contact, separated only by 

 the stratum intermedium, as I have described in connection with 

 the 82 and 83 mm. embryos (fig. 5). To quote from Tomes, 



The destination and function of the stellate reticulum is not very 

 clear. Enamel can very well be formed without it, as is seen amongst 

 reptiles and fish, and even in the mammalia it disappears prior to the 

 completion of the tissue so that a great deal of enamel is formed after 

 the internal and external epithelia have come into contact. 



The enamel which is deposited in the teeth of the armadillo 

 then evidently corresponds to the last formed enamel of other 

 animals, which may be deposited after the disappearance of the 

 stellate reticulum. 



I may state here that I have never observed the presence of 

 blood vessels within the stellate reticulum; the rich supply of 

 blood vessels in the vicinity of the enamel organ of the older 

 foetuses is derived from the surrounding connective tissue which 

 is in direct contact with the cells of the enamel organ. 



As to the ultimate fate of the outer enamel epithelium, and 

 stratum intermedium, I can only say that prior to the formation 

 of enamel, the outer enamel epithelum comes in contact with the 



