Royal Society, 54-1 



tinuation of the dentinal tubes into the enamel ; so far as the author 

 has investigated them, he finds but one exception, and that in the 

 Wombat, — the representative of the rodents in the marsupial order. 

 This creature, he finds, has teeth that are nearly allied in structure 

 as well as external form to the teeth of rodents, and more especially 

 to the Hare and Rabbit. 



The author states, that he has observed that the dentinal tubes in 

 the human and other teeth are sometimes continued for a short 

 distance into the enamel. This he considers a rudimentary condi- 

 tion which is fully developed in the marsupial teeth. The author 

 observes that the dentinal and enamel pulp become firmly united to 

 each other previous to the commencement of calcification in either, 

 and that it is highly probable that the linear columns of the two 

 pulps are joined end to end, and that the columns of the enamel pulp 

 so joined become developed into tubes instead of into solid enamel 

 fibres. He considers this the more probable, as he has observed 

 that the enamel fibres in an early stage of development are partially 

 tubular in the teeth of several animals whose enamel fibres are ulti- 

 mately solid. 



The teeth described and figured are those of the — 



Macropus giganteus. Petaurus sciureus. 



Hypsiprymnus penicillatus. Dasyurus macrourus. 



minor. ursinus. 



y.^ Phalangista vulpina. Thylacinus cynocephalus. 



Wombat. Didelphis virginiana. 

 Petaurus taguanoides. 



The author considers that the facts stated in his paper justify two 

 conclusions of a general character. First, that the existence of pro- 

 longed and fully-developed tubes in the enamel, continuous with 

 those of the subjacent dentine, is common to the great majority, if 

 not all, of the marsupial animals, excepting the Wombat. And, se- 

 condly, that the enamel and dentine are so closely related, that they 

 should be regarded as modifications of each other, rather than as 

 tissues of a wholly different nature. 



" On the Motion of Gases." — Part H. By Thomas Graham, 

 F.R.S. &c. 



The experiments of the former paper by the author on the same 

 subject, afforded grounds for assuming the existence of a relation in 

 the transpirability of different gases, that is, their passage through 

 capillary tubes of an equally simple nature as that which is recog- 

 nized among the specific gravities of gases, or even as the still more 

 simple ratios of their combining volumes. Compared with solids 

 and liquids, matter in the form of gas is susceptible of small variation 

 in physical properties, and exhibits only a few grand features. These 

 differences of property, which are preserved amidst the prevailing 

 uniformity of gases, may well be supposed to be among the most 

 deep-seated and fundamental in their nature with which matter is 

 endowed. Under such impressions he has devoted an unusual 

 amount of time and attention to the determination of this class of 



