DEVELOFMKNT OF TEETH IN HATTERIA PUNCTATA. 169 



spicuous structures. Many of them are well advanced in 

 calcification, and a deposit of enamel has commenced. In fig. 

 3 is shown the enamel organ of the first premaxillary tooth of 

 the right side. The mesodermal papilla indents the deepest 

 portion of the dental lamina at this point, and there is no 

 indication of a lingual continuation of the latter. The 

 enamel epithelium is conspicuous, and evidences of the stel- 

 late tissue are seen, while the mesoderm shows a tendency to 

 form a capsule. In this tooth no calcification has yet 

 occurred, and the odontoblasts are still undifferentiated meso- 

 derm cells. In the second premaxillary tooth, however, there 

 is a considerable degree of calcification, and an indication of 

 a prolongation of the dental lamina on the lingual side can 

 be detected. In both these points the third premaxillary 

 resembles the first. Comparing these three teeth with the 

 corresponding anterior three on each side in the lower jaw, 

 we find that similar relations obtain, i. e. that the second is 

 more advanced than the other two, and shows indications of 

 a lingual prolongation of the dental lamina. I shall have 

 more to say on these points in the sequel. Each maxilla has 

 ten teeth, most of which are more or less calcified ; but here, 

 again, there is a well-marked alternation in the degree of 

 calcification. As sagittal sections only of this embryo were 

 at my disposal, I am unable to give the precise relations of 

 the dental lamina in the lateral regions of the jaws. The 

 mandibular teeth posterior to the first three (eight in number 

 on each side) are, as regards the first six, well calcified, the 

 two posterior only slightly so. 



The anterior end of the palatine tooth-bearing regions is 

 indicated by the presence, on each side, of the tooth of the 

 first series, mentioned in the last section. The dental lamina 

 bears three enamel organs, which show no calcification. 



Embryo R, 162, in about the eighth month of incubation. 

 Although this is apparently so much older than the last 

 embryo, the stage in development is actually not much more 

 advanced, for Dendy (loc. cit.) has pointed out that, for a 

 long period during the winter months, very little progress 



