1888.] Teeth in the young Ornithorhynchus paradoxus. 353 



the equations can be solved ; some special examples are given. For 

 the sake of greater intelligibility, I have included an historical 

 account of previous theories of plane plates and shells, a description 

 of the method of the present paper, and a summary recapitulating 

 the chief physical results. 



II. " True Teeth in the young Omitlwrhynchus paradoxus." By 

 Edward B. Poulton, M.A., F.L.S., of Jesus and Keble 

 Colleges, Oxford. Communicated by W. K. Parker, F.R.S. 

 Received January 26, 1888. 



For the purpose of continuing some recent work upon various 

 epidermic structures in Ornithorhynchus, Dr. Parker very kindly 

 placed his most valuable material at my disposal. Among other things 

 was a series of consecutive vertical transverse sections through the 

 head of a young individual, about 8 "3 decimetres long, when in the 

 curled-up attitude in which it had been received, and which was 

 fixed by the spirit. In this specimen only the larger hairs had 

 appeared above the surface of the skin. 



The sections had been prepared for Dr. Parker by his son, Professor 

 W. Newton Parker, of Cardiff, and although intended for the investi- 

 gation of morphological points in connexion with the development and 

 structure of the skull, many of them were in every way adapted for 

 minute histological investigation. Examining these sections I found 

 that large and apparently typical mammalian teeth were developing 

 in the subepithelial tissues on each side of the roof of the mouth. I 

 at once communicated with Dr. Parker, telling him of the discovery, 

 and enquiring whether he had any objection to the publication of the 

 fact. Dr. Parker replied, and urged me to at once communicate the 

 discovery to the Royal Society, at the same time offering me material 

 in the most free and generous manner for the further investigation of 

 the dental structures in Ornithorhynchus and in Echidna (if present 

 in the latter). When it is remembered that Dr. Parker had put the 

 sections aside for a time in consequence of the press of other work, 

 intending soon to make use of them for the investigation of the skull, 

 it will be seen at once that my association with this discovery is 

 purely accidental, and that I have been treated in an extremely 

 generous spirit. 



As the lower jaw was not included in the sections, I cannot yet 

 state that teeth are present in it, but there is little doubt that this is 

 the case.* Teeth were present in the upper jaw, in thirty sections 

 through the head, and of these all, except the nine anterior sections, 

 included some part of the eye. The teeth probably represent some 



* 1 have since found that teeth are present in the lower jaw. — Feb. 6, 1SS8. 



