THE MAMMALS 133 



many mammals) and nurse from a rudimentary mam- 

 malian milk gland which lacks a nipple. It has a flat- 

 tened, duckhke bill, and teeth are present only in the 

 young as vestigial molars. It is in no way related to the 

 birds, in spite of its bill and the fact that its feet are 

 webbed Hke those of a duck, both characters being sec- 

 ondary. The bill is a soft, kidskinlike leathery expansion 

 of the muffle of the marsupials, and the webbing be- 

 tween the toes is only an exaggeration of that between 

 the human fingers. It is, in short, a grotesque mixture of 

 reptilian and mammalian characters, with some speciah- 

 zations of its own. The platypus's five-toed hands and 

 feet are well adapted to digging, and it hves in burrows 

 along the banks of the streams and lakes of Austraha 

 and Tasmania, feeding on insect larvae, worms and 

 aquatic plants. Its consumption of food in captivity is 

 phenomenal: a four-pound male specimen in the New 

 York Zoological Park consumed daily 20 to 30 live cray- 

 fish (more if available), one frog, a dish of duck-egg 

 custard (1 to 1V2 eggs), and one pound of Hve earth- 

 worms (and only difficulties of supply kept the worm 

 consumption down to this level)— adding up to a gross 

 weight of two and a half to three pounds. Nothing is 

 known, regrettably, about nitrogen excretion in either 

 the spiny anteater or the platypus, nor wiU the alert 

 Zoological Park authorities allow an experimentally 

 minded investigator within less than looking distance of 

 the tremendously valuable animals in its platypusary. 



The second stream of mammalian evolution stemming 

 from the cynodonts led to the Jurassic Pantotheria 

 {panto = all; therion = beast), from which were derived 

 all later mammals, the most primitive of which are the 

 Marsupiaha, or pouched animals, which include the 

 kangaroo and opossum (the latter the most primitive 

 mammal in the northern world)— whose young are bom 

 alive but in such an immature state that they must be 

 carried in a pouch by the mother for a considerable 



