.8^. NOTES AND COMMENTS. 247 



communications to the Anatomischev Anzeiger for 1891, have now 

 afforded a definite solution of the problem. It appears from an 

 examination of some embryos of opossums that the replacing set of 

 teeth is actually present in the jaw, although only one of these teeth 

 ever completely develops and becomes functional. It is also proved 

 rem a study of the embryos of certain armadillos and toothed 

 whales in which no tooth -replacement has been observed, that the 

 replacing set is actually formed though absorbed without use in the 

 adult. In short, we may definitely conclude that mammals originally 

 inherited two sets of teeth from their cold-blooded ancestry — that in 

 some groups such as the toothed whales, some armadillos, and 

 marsupials, the second set of teeth is almost or quite aborted, while 

 in the majority of the higher mammals this set is functional and 

 partly replaces the first set. As a matter of fact, the two series of 

 teeth in the jaw of the embryo always originate by the division of a 

 single series of germs ; and in this respect the mammalian dentition 

 presents some difference from that of the reptiles and batrachians. 

 There are, moreover, other points still awaiting elucidation, as 

 remarked in a critical article by Mr. Oldfield Thomas in the April 

 number of the Annals and Magazine of Natural History. 



Palaeontology, as usual, may be expected sooner or later to assist 

 in the solution of the remaining difficulties ; and it is interesting to 

 notice in the May number of the American Journal of Science (vol. 

 xliii., p. 446) that Professor Marsh has already a small contribution 

 to the subject. In describing the primitive Eocene mammals, 

 Hyracops and Meniscotherium, the Professor remarks that the replace- 

 able first set of teeth remains in use long after the appearance of the 

 three permanent molars, thus suggesting that the latter are actually a 

 retarded portion of this first set, and not part of the second series. 



The Australian Marsupial Mole. 

 Last month we briefly quoted Professor Cope's observations on 

 the affinities of the much-discussed Notoryctes,^ but refrained from 

 comment in view of Dr. Hans Gadow's promised contribution to the 

 Zoological Society. The results of Dr. Gadow's personal examina- 

 tion of the original specimens brought to England by Professor 

 Stirling were presented to the meeting of this society on May 3, and 

 we congratulate Professor Stirling on the manner in which his work 

 in a distant colony has been confirmed by the subsequent researches 

 in the Museum of Comparative Anatomy at Cambridge. Dr. Gadow 

 recognises the functional pouch and the mammae placed within ; he 

 finds the peculiar arrangement of the urinogenital organs of the male 

 so well known in the Marsupials ; and he notes certain skeletal 

 characters that indicate affinities with the same order. In short, Dr. 

 Gadow finally disposes of all doubts as to the non-placental character 



^ Supra, p. 167. 



