Embryology. 369 
distinct. No enamel is formed from them at this stage, except, 
probably, in the case of the most anterior tooth. The dentine-germ 
was found quite normal in appearance; the depressed, superiorly 
conical pulp-mass resembles that seen in other Mammalia, and, as 
in some other forms, this is to some extent embraced around the 
sides and below by the in-curved lower edges of the dome-shaped 
enamel organ, which, as in other forms, is superimposed upon the 
pulp. Dentinal tubules and odontoblasts can be made out in the 
vicinity of the apex of the pulp-mass. 
ere can be little doubt that these structures are characteristic 
mammalian teeth, as supposed by their discoverer. Hertwig’s 
researches serve to show that mammalian teeth ‘are probably in a 
more ancestral condition than any other organ by the 
ancestors—and yet existing Prototheria were not known to possess 
them. Their occurrence in Ornithorhynchus, therefore, supplies the 
step just where it is wanted ; and the fact that they are practicall 
identical with the young teeth of higher mammals is a further indi- 
cation of the ancestral nature of these structures; for other higher 
mammalian features represented in the Prototheria are profoundly 
modified in the latter. 
Mr. Poulton, in conclusion, announces his intention of tracing 
the further fate of the teeth of Ornithorhynchus in later stages, for 
which purpose Dr, Parker has also placed additional materials at 
his disposal. 
THE ECTOBLASTIC ORIGIN oF THE WoLFFIAN Duct IN CHE- 
LoNIA.'—In a note with the above title, K. Mitsukuri, of Tokio, 
Japan, gives a short account of his researches upon the develop- 
ment of the segmental ducts of Trionyx japonica (Schleg.) and Emys 
pi flotin (Gray). The author has found stages which show that the 
olffian duct arises from cells proliferated from the ectoblast, just 
opposite the region of the intermediate cell-mass. As described by 
others in other forms, these ducts in Chelonians are found by 
Mitsukuri to develop from before backwards. 
ti Aa OF THE WOLFFIAN DUCT IN LacERTILIANS.—Inves- 
gations upon the development of Lacerta agilis, L. lis, 
and . viridis by J. von Perenyi? confirms and extends his obser- 
` Vations upon the ectoblastic origin of the segmental ducts in this 
and other forms. Interesting observations are also recorded by 
Perenyi in the above-cited note on the development of the amnion 
and allantois of Lacerta. 
, Zoolog. Anzeiger, XI, 1888, No. 273, p. 111. 
* Zoolog. Anzeiger, XI, 1888, No. ord a 138-141, 
