The researches of Goodsir, constituting as they did a very material advance in knowledge, became so deeply graven upon the minds of scientific men that subsequent investigations, tending to modify his conclusions in important particulars, have attracted less attention than is their due. As long ago as 1853 Professor Huxley (Quart. Journ. Microscop. Science, vol. i.) published the statement that, in the frog and mackerel at all events, the tooth-germs are at no time in the condition of free papillæ; and in the same paper correctly described the connexion existing between the oral epithelium and the enamel-organ in the fully formed dental sacs. Thus, although Professor Huxley accepted as in most particulars accurate the account given by Goodsir of the sequence of events in the formation of the human tooth-sac, he in some degree anticipated the discovery made by Professor Kölliker some years later (Zeitschrift f. wiss. Zool. 1863), that in several Mammalia the tooth-germs never pass through any papillary stage, but are from the first deep below the surface.