Sub-Class HI.— Ornithodelphia. 



Order 13. Monotremata . . . Platypus and echidna. 



As to the mode of succession in which these various 

 orders may have been evolved we can as yet only make 

 more or less plausible conjectures. 



On the whole it seems probable that the Insectivora — 

 especially such a form as that spineless hedgehog, gym- 

 nura — may amongst existing animals give us the best 

 general idea of primitive mammalian life. 



Certain marsupials seem closely allied to insectivores, 

 and may have been a lateral offshoot from ancestral 

 insectivorous forms. 



The platypus and echidna show characters which 

 point down below the whole class of beasts and towards 

 reptiles, but they are animals of very peculiar formation, 

 and there seem to be no other existing beasts which 

 have any special relationship to them, save perhaps some 

 of the edentates. But these again are specially modified 

 forms, and our speculations are here, as in so many other 

 instances, checked by the probability of the independent 



origins of similar structures. 



