28 



Mr. C. S. Tomes. On the Development of 



genera will not only accord with, but appears actually to support a 

 view of septation. 



For the analogy with septate anthers, where septation must have 

 occurred, and the similarity between the details of these and those in 

 Dancea, and especially the partial septations in both, make it appear 

 probable that in this genus progressive septation has taken place. It 

 is thought probable that progressive septation has been a feature, at 

 least where the sori are elongated, as in Dancea. But the question 

 is left over for future discussion whether or not a similar septation, 

 rather than coalescence, may be accountable also for the origin in 

 the first instance of a circular sorus with a plurality of sporangia 

 united together as in Asterotheca, or in Pecopteris unita. 



" On the Development of Marsupial and other Tubular 

 Enamels, with Notes upon the Development of Enamel in 

 General." By Charles S. Tomes, M.A., F.R.S. Received 

 July 12, 1897. 



(Abstract.) 



It was pointed out by my father, the late Sir John Tomes, that 

 the enamel of marsupials was peculiar in that in the whole class, 

 with the solitary exception of the Wombat, the enamel is freely pene^ 

 trated by tubes which enter it from the dentine, and are continuous 

 with the dentinal tubes at the junction of the two tissues. This 

 character is met with sporadically in other mammals — for example, 

 in the Jerboa among rodents, in the Shrew among insectivora, and 

 notably in the Hyrax, in which animal the free penetration makes its 

 enamel look quite like that of a marsupial. 



Whilst there is a large literature upon the development of ordinary 

 enamel, little or nothing has been written about that of tubular 

 enamels. 



The outermost portion of marsupial enamel is always devoid of 

 tubes, and the extent to which the tube system exists varies greatly 

 in different members of the group, so that the same enamel organ is 

 obviously capable of forming either tubular enamel or enamel with 

 solid prisms. Moreover, the sporadic reappearance of tubular 

 enamels amongst mammals who have for the most part lost this 

 character, and its occasional occurrence in a rudimentary condition 

 as an abnormality in man, point to its not originating in any manner 

 fundamentally different from that of ordinary enamel development; 

 and it is claimed that the study of its development in marsupials 

 affords the clue to the real nature of enamel development in all 

 animals. 



