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SCIENCE. 



[jST. S. Vol. II. No. 47. 



tober 18th an excursion to Popotla was 

 made by wagons, starting from ' la Plaza de 

 la Constitueion,' opposite the ' Portal de 

 Mercaderes.' 



This was chieflj' a visit ' al arbol de la 

 Noche Triste,' the famous tree against 

 which Cortes rested and wept on the night 

 of his terrible defeat. The tree, unfortu- 

 nately, seems dying, but its tremendous 

 trunk, a wooden tower, may still be a land- 

 mark for centuries. 



The tree of Montezuma, at the back of 

 Chapultepec, is still flourishing, one the 

 grandest and most impressive of living 

 things on this earth. 



At ten o'clock a visit was made to ' la 

 Escuela Nacional de Ingenieros,' where is 

 perhaps the greatest collection of large 

 meteorites in the world. 



At four o'clock again in session in the 

 Escuela Prepartoria. 



But already we have followed long enough 

 to give an insight into the life of this most 

 enjoyable Congress, and while the fortunate 

 American istas go south by rail to Oaxaca, 

 thence to ride to Mitla, digging in the pre- 

 historic past, we face again the unsoftened 

 raw newness of our own United States. 

 George Beuoe Halsted. 



Austin, Texas. 



RECENT INVESTIGATIONS UPON THE EM- 

 BRYOLOGY AND PATHOLOGY OF TEETH. 

 The embryonic development of the teeth 

 is now a subject of most active investiga- 

 tion, and we are constantlj^ receiving new 

 communications from Leche, in Stockholm; 

 Kiikenthal,in Jena, and Rose, in Freiburg. 

 The most striking discover}' is that of the 

 existence throughout the mammalia of 

 remnants of two series of teeth, preceding 

 the milk and permanent series. The 

 teeth represented in these two series are 

 entirely vestigial ; both precede the embry- 

 onic development of the milk teeth, and 

 are indicated merely by indentations of the 



dental fold. So far as known, these germs 

 never develop enamel, but they constitute 

 the most positive evidence of the deriva- 

 tion of the mammalia from reptilian or am- 

 phibian ancestors with a multiple dental 

 succession. These ' prelacteal ' teeth, as 

 they are called, were first observed by Leche, 

 in 1892, in certain Insectivora, but they 

 have subsequently been found among the 

 Marsupialia and in the seals. Eose has now 

 found unmistakable vestiges of these teeth in 

 the human jaw. Man, therefore, in com- 

 mon with many other mammals has four sets 

 of teeth, instead of two as formerly supposed. 



R5se's investigations upon the teeth of 

 Amphibia Eeptilia and fishes demonstrate 

 conclusively the truth of Hertwig's theory 

 that teeth are modified scales which have 

 passed into the mouth cavity. He finds 

 that the rudiments of the first series of 

 teeth in each of these types develop exactly 

 after the manner of the placoid dermal 

 scale. The second series of teeth develop 

 after an intermediate type, and it is only 

 the third series of teeth which develop from 

 the typical dental fold lying suspended 

 within the mesoblast, or lower tissue of that 

 layer. Dr. Eose, with Prof. Kiikenthal, of 

 Jena, has been the most active supporter 

 of the theorj' of the origin of complex tooth 

 crowns bj' concrescence of primitively sep- 

 arate cusps, and this ' concrescence theory ' 

 has spread very rapidly in Germany as an 

 explanation of the mode of origin of the 

 elaborate tooth forms. There are very slight 

 grounds of evidence for it among the mam- 

 malia; in fishes, however, it has long appear- 

 ed probable that the well-known tj'pe of shark 

 tooth (Lamna), consisting of three cusps 

 united at the base, so abundantlj' found in 

 the phosphate beds of South Carolina, rep- 

 resents a concrescence. Eose has now made 

 a very careful study of the tooth develop- 

 ment of Chlamydoselachus anguineus, Garman, 

 and finds conclusive evidence that the com- 



