40 CHARLES S. TOMES. 



figs. 2 and 28) . It'now appears that this stellate condition is 

 assumed also by the more common biscuit- shaped plastids. 



The second additional form of aggregation was observed 

 very abundantly in Mr. Archer's gathering of B. rubescens. 

 It may be described as cylindrical. Suppose a number of 

 stellate aggregates superimposed and you have a cylinder. 

 These cylinders are often six or seven times as long as they 

 are broad. 



On the Development of Teeth. By Charles S. Tomes, 

 M.A., Lecturer on Dental Anatomy at the Dental Hos- 

 pital of London. With Plates IV and V. 



For many years past it had been thought that, in its broad 

 outlines at least, our knowledge of the development of teeth 

 was accurate ; few persons have hence devoted their time to 

 the verification of the current descriptions, and even now, 

 though several years have passed since Kolliker and others 

 first published their results, and proved that inaccuracies of 

 moment existed in the received accounts, the old theories still 

 hold sway in most of our text-books. 



This being the case, I propose to |give a short outline of 

 the leading facts in tooth development as they are at present 

 known, not confining myself to my own researches (which 

 relate chiefly to the teeth of reptiles, amphibia, and fishes), 

 which are more fully detailed in papers published in the 

 * Philosophical Transactions.' 



In the papers referred to, and in a manual of dental 

 anatomy now in the press, I have given full references to the 

 authors who have of late years contributed to onr knowledge 

 of the subject; and I will, therefore, not attempt to do more 

 in the present communication than allude to a very few of 

 their more important papers. 



Until within the last few years the researches of Goodsir 

 were taken as the foundationof our knowledge of the develop- 

 ment of human and other mammalian teeth, and the generali- 

 sations of Professor Owen as authority for the modifications 

 to be met with among reptiles and fish. 



The starting-point of Professor Owen's generalisations hap- 

 pened, however, to be just that portion of Goodsir's descrip- 

 tion which is not quite in accord with the facts since observed, 

 so that subsequent investigations controvert very much that is 



