THE PHYLA HEMICHORDATA AND CHORDATA 



The Metatheria, such as the kangaroos and opossums, give birth to young 

 which are minute and in a relatively undeveloped state; these young are then 

 transferred to a brood pouch or marsupium until development is completed 

 (Fig. 18.31). In the Eutheria the young are attached to the mother's uterus 

 by the placenta and are thus nourished until they are born in more advanced 

 stages, ranging from blind and hairless mice to colts that stand and run with- 

 in a short time after birth. The Metatheria may be regarded as survivors of 

 an evolutionary stage intermediate between the egg-laying ancestors and the 



Fig. 18.34. Representative lemuroid Primates. A, Tupaia, a tree shrew; this primitive 

 primate type exhibits characteristics which indicate the common ancestry of modern primates 

 and insectivores. 5, tarsiers, Tarsius, and C, a "bush baby," Galago; these are arbo- 

 real, nocturnal primates. The modern lemuroid primates are representatives of an 

 evolutionary stock believed to have diverged from the anthropoid line in Paleocene- 

 Eocene time. (Photographs courtesy New York Zoological Society.) 



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