78 Enamel in the Teeth of an Embryo Edentate 



were observed. The point Ballowitz lays most stress upon is the finding 

 of an epithelial ring at the base of the dental papilla which is a portion 

 of the enamel organ constricted off from the lower edge of that organ. 

 He has shown this epithelial ring to persist in the adult, and he regards 

 it as essential to the development of the dentine in these continuously 

 growing teeth. He quotes from A. von Brunn's work on the enamel 

 organ in support of this theory, but I have been unable to see this 

 article. Ballowitz denies that the presence of the stellate reticulum 

 and stratum intermedium have any close connection with the deposition 

 of enamel, stating positively that at no time can enamel be deposited 

 in the Dasypus novemcinctus, and that the only functions of the enamel 

 organ are : to give form to the developing tooth, to stimulate the odon- 

 toblasts to deposit dentine, and to give off the epithelial ring which is 

 necessary to the continued development of the dentine. 



A year ago. Dr. W. M. Wheeler, of the School of Zoology, had the good 

 fortune to secure four embryos of the Dasypns novemcinctus from an 

 adult female which had been kept in the laboratory for several weeks. 

 The embryos were removed immediately after the animal had been chloro- 

 formed, and were hardened for six weeks in Miillcr's fluid, primarily for 

 studying the placentation. He found four placentae inclosed in one 

 amnion (Plate I), but has not since had the time to study the subject 

 further. Dr. Wheeler very kindly furnished me the material for work- 

 ing on the embryology of the teeth, but owing to the pressure of other 

 work, nothing was done until this year. 



The largest embryo of 9 cm.' and one measuring 8.5 cm. were selected. 

 From the larger embryo, longitudinal sections of the lower jaw were 

 made, and by making a sagittal section of the upper jaw, both longi- 

 tudinal and transverse sections were obtained. They were imbedded 

 in celloidin, cut 25 micra thick, and stained in hasmatoxylin and 

 eosin, but were not kept in series. From an embryo of 8.5 cm. both 

 longitudinal and transverse sections of the lower jaw and longitudinal 

 sections of the upper jaw were made. They were imbedded in paraffin, 

 cut 10 micra thick, mounted in series, and stained with iron hsema- 

 toxylin. 



In the longitudinal sections of the lower jaw of the 8.5 cm. embryo, 

 I found five rudimentary incisors and eight back teeth. The jaw 

 measured 11 mm. from the tip to the posterior edge of the last tooth- 

 bud. The first incisor was found 1.8 mm. from the tip, the width of 



" In all cases the measurements jjiven are from the crown of the head to the base 

 of the tail. 



