8 MAMMALIAN DESCENT. [Lect. I. 



in which there are characters much more archaic than 

 anything seen in SerjDents, Lizards, Tortoises, Crocodiles, 

 or in Emeus. Therefore the existing reptiles and birds 

 must stand aside as havino- nothino; to do with the 

 family tree of the Monotremes, although in some things 

 they are like these beasts, and many of their organs are 

 formed on a similar pattern ; they are all equally below 

 the morphological level of the nobler Mammalia. 



Although some of the mammalian characters are well 

 marked out in the Monotremes, yet they only agree with 

 the higher Mammalia to a very limited extent ; some 

 things now seen in them are quite new to me. 



Most of the existing fishes have ceased, or nearly 

 ceased, to begin life in a larval form, or one lower than 

 that in which they spend the main part of their existence. 

 Some degree of metamorjDhosis is seen in the Ganoids, 

 and more in the Lamprey ; but T\dth the Amphibia 

 (Newts and Salamanders, Frogs and Toads), it is in the 

 larval, or gruh-stage, that we find the oldest things. 

 One kind of frog, from the Cape, is the first creature 

 that is possessed of nails to its toes and fingers ; it is 

 termed Dactylethra. The tadpole of this frog has 

 shown me some of the most archaic structures, and 

 the lowest condition of the tissues themselves, that 

 I have met with in the whole sub-kingdom of the 

 Yertebrata. 



I speak of this for two reasons : — first, I find things 

 in it which are quite like what are to be seen in the 



