378 On the possibly Dual Origin of the Mammalia. [Feb. 10, 



Pike, and certain fishes yet undescribed. The poison fangs of Serpents 

 have also arisen independently, as is certain when we compare the fang of 

 Atractaspis with that of Viper a ; quite independently also have arisen 

 the poison teeth of Heloderma. The scrotum of placentals and the 

 singularly placed scrotum of marsupials (so difficult to explain either 

 by "natural" or "sexual" selection) must also have had a dual 

 origin, as the prehensile pes of Didelphys and of the Apes has also 

 doubtless had. For my own part I am still disposed to maintain the 

 probability, which I long ago asserted, of the independent origin of 

 the Simiadm and the Cebidce, and now Professor Cope brings forward* 

 noteworthy reasons for believing that the Horse of America and the 

 Horse of Europe have had a widely distinct ancestry, and have grown 

 alike from two distinct lines of descent. Finally I would refer to the 

 similar forms of placenta, both umbilical and allantoic, which seem to 

 have arisen independently, as also have the mammary glands of Mono- 

 tremes and other mammals. Any one who is disposed to think in- 

 credible the independent origin of a mammalian molar in a diverging 

 offshoot from the Sauropsidan tree, I would ask to bear in mind 

 the multitude of origins which we must regard as independent, 

 and often as quite geologically modern. Among them I would 

 enumerate the dentition of Desmodus, Diphylla, and Cheiromys, and 

 especially the very remarkable multicuspidate canines of a Pteropine 

 bat (Pteralopex atrata) recently described! by Mr. Oldfield Thomas. 

 What again can be more singular than the wonderful dental diver- 

 gence between the Narwhall and the Beluga, otherwise so extremely 

 alike in structure ? The poison teeth and, as we shall soon learn, the 

 poison gland and ducts of Heloderma, before referred to, are also most 

 noteworthy. Again, what is more startling than to find the respiratory 

 tail of the young Hylodes and the respiratory ventral folds of Sana 

 cpisthodon ?J The tip of the snout of the young of this animal 

 reminds us of the beak of the unhatched chick, though there can be 

 doubt but that these structures have arisen independently. The 

 development of this Batrachian recalls to mind the similarity of con- 

 dition of the Axolotl, the larvae of Triton alpestrij, and the so-called 

 Per enni branchiate Batrachians, all of which seem to have acquired a 

 normal or permanent condition of life resembling that of immature 

 stages in the existence of their several ancestors. 



Mr. Boulenger has been kind enough to inform me of another case 

 of the sudden origin of a new character — probably a reversion — which 

 he has noticed in a Lizard, a species of Gymnophthalmus. Here nor- 

 mally the tail is clothed with scales, quincuncially disposed, as in the 



* See ' American Naturalist ' for December, 1887. 

 t See ' Ann. Mag. Nat. Hist.,' toI. 1, 1888, p. 155. 



X See Mr. Boulerger's paper on the reptiles and batrachians of the Solomon 

 Islands, ' Zool. Soc. Trans.,' toI. 12, p. 51. 



