MAMMALIA 



375 



apertures upon two mammary areas each about one half inch in 

 diameter. The young scrape and suck the milk from these areas. 



Young duck-bills feed upon Crustacea, insects and worms. On 

 each hind foot, male duck-bills, or duck-moles, have a sharp horny 

 spur with a poison gland connected. 



Fig. 211. Platypus. (Courtesy of N. Y. Zool. Soc.) 



Fossil Relatives of the Monotremata. — Monotremata are found 

 in the Pleistocene, and it is possible that the doubtfully mammalian 

 types of Protodonta, Dromatherium and Micronodon^ of the Upper 

 Triassic, are also related. 



Order 2. Marsupialia. — Viviparous, usually carrying their 

 young (born in a rudimentary condition) in a marsupium or pouch; 

 allantoic placenta usually absent. Small eggs undergo a total 

 segmentation in most species, and develop in the maternal uterus, 

 nourished by a secretion from its walls. The ventral surface 

 is supported by the marsupial bones, slender rods articulated right 

 and left, at the pubic symphysis. Corpus. callosum absent. 



