242 VERTEBRATA. 



in the lizards. Marsupial bones [wrongly so called, Huxley'] art 

 present, but there is no marsupial pouch. There are no external 

 ears. The corpus callosum is wanting, and the optic lobes are 

 simple or undivided. 



Of the two genera, Echidna is terrestrial, with beak-hike jaws, 

 and a small mouth at the end, a long slender tongue, and a body 

 covered with spines, and with an exceedingly short or almost 

 obsolete tail ; the male has a perforated spur. There are two 

 Australian species, and one or two from New Guinea. It is 

 doubtful if the species are oviparous or ovoviviparous. Orni- 

 thorhynchus is aquatic, with a flat duck-like beak, short tongue, 

 mole-like fur, and a broad flat tail of moderate length. A single 

 Australian species is known the duck-mole or water-mole ( Orni- 

 thorhynckus paradoxus). It is a good swimmer and constructs 

 long burrows in the banks of rivers ; it feeds like a duck, sucking 

 up its prey from the mud. 



Echidnidce. Ornithorhynchidce. 



Echidna = Tachy glossus. Oraithorhynchus = Platypus. 



Order II. MAESUPIALIA. 



DlDELPHIA. 



An abdominal pouch in the female. True teeth of two or three 

 kinds. No common cloaca. No placenta. 



The abdominal pouch [marsupium] is supported by the mar- 

 supial bones, which are ossifications of the inner tendon of the 

 external oblique muscle. It is into this pouch that the prema- 

 turely born offspring is transferred, the young animal remaining 

 suspended from the nipple, and so helpless as to be unequal to 

 the muscular effort of sucking. The mother, however, has the 

 mammary gland provided with a cremaster muscle, by which she 

 is able to force her milk into the mouth of her pendent young. 

 The marsupial bones occur also in the males, but without the 

 pouch. The coracoid, as in the higher Mammalia, forms part 

 of the scapula, and is not attached to the sternum. The corpus 

 callosum is very small or wanting. The size of the brain is ^ in 

 Pefaurisfa pygmcea, and T ^ in Macropus major. 



The fore and hind limbs are somtimes connected by an exten- 

 sion of the integument from the side, as in Petaurus and Acrobata. 

 In Chironectes, the only aquatic form, the feet are webbed. The 

 opossums have on their hind feet a thumb opposable to the digits, 

 as in the Quadrumana. 



