MAMMALIA 303 



Order 8. Ungulata. Hoofed animals. 

 Order 9. Sirenia. Manatee and dugong. 

 Order 10. Primates. Monkeys, apes, man. 



653. The Monotremata are the most primitive mammals. The embryo 

 is not nourished in a uterus. An egg is laid from which the embryo hatches 

 in a very immature condition. It is then nourished from the mammary 

 glands. The long snout is covered by a horny sheath like a duck's bill. 

 There are no teeth in the adult. The mammary glands have no nipple. 

 Many reptilian characters are presented as, e. g., in the presence of a 

 coracoid bone, a cloaca, a variable body temperature, the slightly devel- 

 oped corpus callosum, the condition of the reproductive organs, etc. 

 The Monotremes are found only in Tasmania, Australia and New 

 Guinea. 



654. The Marsupialia, with exception of the American opossum, are 

 also confined to Australasia. There is no placenta and the young are 

 born in a very immature stage. They are then placed in a sack formed 

 by a fold of the skin covering the region of the mammary glands. Here 

 the young attach themselves to a nipple and continue their development. 

 The pouch is supported by two bones. 



655. The Polyprotodontia are carnivorous or omnivorous Marsupials. 

 They have a well-developed set of teeth of the four kinds. 



656. The Diprotodontia are vegetable feeders and the teeth are not 

 developed as a full set. 



657. The Monodelphia have no pouch. The fcetal membranes form a 

 placenta which becomes attached to the wall of the uterus thus forming 

 an organic connection between the embryo and the tissues of the mother. 

 By means of the placenta the embryo is nourished for a period within the 

 uterus. After birth it is nourished from the milk of the mammary glands. 



658. The Insectivora have a full set of pointed teeth. The feet usually 

 are five toed and the toes clawed. The foot is plantigrade. 



659. The Chiroptera have wings formed by a membrane of skin stretch- 

 ing between the greatly elongated fingers and the side of the body. In 

 some cases the eyes are large and the ears small, in others the eyes are 

 small and the ears large. Some are fruit eaters, others catch insects. A 

 few are blood sucking. 



660. The Rodentia are characterized by the long, sharp, chisel-shaped 

 incisors. There are no canines. Rabbits, squirrels, beaver, pocket 

 gopher, mice, rats, guinea pig. 



66 1. The Edentata are either without teeth or have poorly developed 

 teeth without enamel. Scaly ant-eater, armadillo, ant bear. 



