The Tetrapoda: Mammals 631 



a cloaca, no pinna, a penis which conducts only sperm, and oviducts 

 which enter the cloaca separately. The mammary glands are only 

 diffuse glands on the ventral surface of the body ; the young must lap 

 the milk. 



There are three genera in this order, the best known of which is 

 Ornithorhynchus, represented by 0. anatinns, the duck-billed platypus 

 of Australia. 



The adult male platypus is about 24 inches long and the body is 

 covered with a thick grayish brown, velvety fur. The beak is shaped 

 like a duck's bill and is covered with a leathery material. The feet are 

 webbed, and the hind foot of the male has a spur connected to a poison 

 gland. The tail is very short. 



During the day, the platypus remains in a burrow dug in the bank 

 of some stream; they emerge at night to feed upon worms, crayfish, 

 snails, and other small aquatic animals of which they consume tremen- 

 dous numbers. The nest, formed of plant materials, is made in an en- 

 larged chamber at the end of the burrow. Here the two or three 

 small eggs are incubated by the female. They hatch in about two 

 weeks. The small young (about one inch in length) are quite helpless. 

 They are nursed by the female until they have attained a size nearly 

 equal to that of the parent. 



The other two genera in this small order are Tachyglossus and 

 Zaglossus. They are generally known as the spiny "anteaters." Both 

 have as their chief item of diet ants or termites. Both carry their egg 

 in a special pouch rather than placing it in a nest. 



Order Marsupialia. — The marsupials, like the monotremes, seem 

 like relics from an ancient past, for the young are carried in a pouch 

 on the belly of the female. The young are born after a very brief gesta- 

 tion period, and emerge from the vagina as "larvae." They more or 

 less "swim" through the mother's hair to the pouch where they attach 

 to a nipple. Here they remain attached for a period of time, complet- 

 ing their development. Since they are too immature to suck, the mother 

 actually pumps the milk into their attached mouths. In addition to the 

 marsupium or pouch, these animals have other unique characteristics; 

 usually there is no placenta, the female has a double vagina and uterus, 

 and the incisor teeth are not equal on the two jaws. 



At one time, the marsupials were widely distributed over most 

 of the world. At present, however, most are confined to Australia, 

 and the neighboring islands. In the New World, several species still 



