2 J. P. HILL. 



PAGE 



Chapter VI.— General Summary and Conclusions . 79 



Chapter VII.— The Early Ontogeny of the Mammalia 



IN the Light of the foregoing Observations . 85 



1. The Early Development o£ the Prototheria . 86 



2. Tlie Early Development of the Metatheria and 



Eutheria . . . .96 



3. The Entypic Condition of the Eutherian 



Blastocyst . . • .111 



Addendum ...... 121 



List of References ..... 122 



Explanation of Plates ..... 125 



Introduction. 

 " In mammalian emhryology very many surprises are yet in store for 

 ns " (Hubrecht, '08). 



The present contribution contains an account of the prin- 

 cipal results and conclusions at which I have arrived after a 

 somewhat protracted and much interrupted study of an 

 extensive collection of early developmental stages of Marsu- 

 pials, ranging from the fertilised egg to the blastocyst in which 

 the two primary germ layers are definitely established. I 

 believe I am now able to give for the first time an account of 

 early Marsupial ontogeny, based on the examination of an 

 adequate material, and both consistent in itself and witii what 

 we know of the early development in the other two Mamma- 

 lian sub-classes. The material at my disposal was obtained 

 during my tenure of office in the University of Sydney, and 

 with the aid of grants from the Royal Society and of a George 

 Heriot Research Fellowship. It represents the proceeds of 

 some eight years' collecting, and compi'ises a fairly complete 

 series of stages of the native cat (Dasyurus viverrinus), 

 together with a few early stages of other Marsupials, notably 

 Perameles and .Macropus. 



Dasyurus proved in many ways a convenient subject for 

 embryological purposes. It cii,n readily be trapped in many 

 districts in New South Wales; it lives and breeds fairly well 

 in captivity, and though always somewhat intractable, it can, 

 owing to its size, be easily handled, and so may be subjected 



