Geological Society. 503 



minute anatomical structure of the tusks of Mastodontoid animals ; 

 and for having placed at his disposal a copy of the Swedish edition 

 of Retzius's demonstration of the typical structure of the dental or- 

 gans of animals. 



Availing himself of the able tuition afforded by the Swedish Pro- 

 fessor, Mr. Nasmyth says, he has prosecuted the subject, and that 

 these inquiries, besides explaining to him the structure of that portion 

 not completely investigated by Iletzius, have unfolded to him some 

 observations which are now generally acknowledged to be truths in 

 the valuable but intricate department of animal development. He 

 further says, that he has been led to results differing somewhat from 

 those of Retzius, so far as the physiology of the cellular tissues is 

 concerned j yet the general appearances exhibited and the manner 

 of displaying them will remain, he adds, lasting memorials of the ta- 

 lents and ingenuity of the Swedish Professor. 



The specimens to which Mr. Nasmyth's attention has been directed 

 form part of the collection of Mr. Koch, and they were delivered to 

 him as belonging to Mastodon giganteum, Tetracaulodon Godmani, 

 T. Kochii, T. Tapiroides, and the Missourium. In the analysis of each 

 specimen he considers— 



1st, The constituent structures of the tusk. 



2nd. The comparative extent of each of the constituent structures, 

 as far as it can be ascertained. 



3rd. Each constituent structure regarded separately in its minute 

 and individual elements. 



4th. The conclusions derived from the premises as to the place 

 which the animal should occupy in zoological classifications. 



The principle upon which this mode of analysis is based, is that of 

 the infinite variety which nature affects from limited materials, while 

 the constancy of each variety throughout the same species is perfect, 

 This constancy extends, Mr. Nasmyth observes, not only to the con- 

 stituent structures of each tooth, but to the extent of each constituent, 

 as well as to the peculiar arrangement of the minute elements of 

 which each of these structures is composed. 



The examination of each tusk evinces so marked and peculiar a 

 structure, that a cursory inspection will, the author thinks, sufficiently 

 demonstrate specific distinctions, which he supposes must have been 

 accompanied by concomitant peculiarities of organization subser- 

 vient to separate and distinct habits. 



In the following descriptions the word corpuscule is used to desig- 

 nate those appearances constituting the characteristic of bone, but 

 denominated by Retzius cells, because the author is persuaded that 

 those appearances are truly of a corpuscular character ; and the word 

 cell is used to designate the structure of the interfibrous material 

 which was left almost entirely out of account by Retzius, and de- 

 scribed by others as structureless, but demonstrated by the author to 

 be most characteristically organized in the different groups of ani- 

 mals. The term Jibres is used, moreover, to define those appearances 

 which Retzius considers due to a tabular structure, because the au- 

 thor has been unable to find anything which confirms this theoretical 



