4 MAMMALIAN DESCENT. [Lect. I. 



of tlie Secondary epoch we get various remains of the 

 group above the Monotremes — the Marsupials. 



Professor Huxley's classification of the mammals is as 

 follows : — 



1. Pro^o^Aena, or the Monotremes : examples — Duch- 

 hill and Echidna, 



These are the lowest mammals known ; they have 

 uddei^, or milk-glands, but no teats, and in many 

 things stand on the same level as the Sauropsida 

 (re^^tiles and birds). 



2. Metatheria, or the Marsupials : examples — Opos- 

 sum, Phalanger, Kangaroo. These have, besides the 

 milk-glands, perfect teats, but their young are born 

 so early that they derive no direct nourishment from the 

 mother until they are placed on the teat. 



2. Eutheria. — These forms are the highest, and their 

 young do derive direct nourishment from the mother 

 for a considerable time before birth — before they are 

 nourished by milk. In this group we have Moles and 

 Men, and all the forms that lie between these two 

 extremes. I shall speak of the Mole as a low Eutherian, 

 of Man and of his Horse as high Eutheria. 



There are at present three groups of labourers working 

 at the Mammalia ; as, indeed at other t}^3es also ; these 

 are : — 



1. The Zoologists. These study the finished form, 

 habits, and distribution of the various types, in the 

 Ijresent state of the planet. 



