SURVEY OF THE ORDERS OF MAMMALIA. 679 



The development of the fertilised ovum is in most respects 

 like that of the hedgehog (pp. 648-56). In the guinea-pig 

 and some other Rodents, out not in the rabbit, there is a 

 remarkable inversion of the germinal layers. 



There is in the rabbit, as in all Rodents, a provisional 

 yolk sac placenta. The allantoic placenta is discoidal and 

 deciduate. 



SYSTEMATIC SURVEY OF THE ORDERS OF MAMMALIA. 



I. Sub-Class PROTOTHERIA or ORNITHODELPHIA Order 



Monotremata. 



II. METATHERIA or DIDELPHIA 'Order Mar- 

 supialia. 



III. EUTHERIA Or MONODELPHIA Or PLACEN- 



TALIA. 



Orders of EUTHERIA. 



1. Edentata. 



2. Sirenia. 



3. Ungulata. 



Hyracoidea. 

 Proboscidea. 

 Extinct sub-orders. 



4. Cetacea. 



Mystacoceti baleen cetaceans. 

 Archceoceti (extinct types). 

 Odontoceti toothed cetaceans. 



5. Rodentia. 



Simplicidentata. 

 Duplicidentata. 



6. Carnivora. 



Carnivora Vera. 

 Pinnipedia. 

 Creodonta (extinct). 



7. Insectivora. 



Insectivora Vera. 

 Dermoptera. 



8. Chiroptera. 



Megachiroptera. 

 Microchiroptera. 



9. Lemuroidea. } =Primates . 

 10. Anthropoidea. j 



