4 MAMMALIAN DESCENT. [LECT. I. 



of the 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. Prototheria, or the Monotremes : examples Duck- 

 bill and Echidna. 



These are the lowest mammals known; they have 

 udders, or milk-glands, but no teats, and in many 

 things stand on the same level as the Sauropsida 

 (reptiles 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 types also ; these 

 are : 



1. The Zoologists. These study the finished form, 

 habits, and distribution of the various types, in the 

 present state of the planet. 



