578 ON THE EARLY STAGES IN THE DEVELOPMENT OP THE EMU 



It will be superfluous to preface the account of these observations 

 with any general resume of previous investigations and theories on 

 avian embryology. This has been done with sufficient thoroughness 

 from different standpoints by Kolliker, Balfour, Wolff, Koller, 

 Duval, and others ; and I shall merely allude in their place to such 

 points in the literature of the subject as are suggested by these 

 observations on the emu. 



For comparison I have used only the common fowl ; and for 

 the most part the methods employed were the methods of treat- 

 ment and preparation followed in the study of that bird*, with 

 such modifications as were rendered necessary by the larger size 

 and different consistency of the yolk. The eggs of the emu were 

 incubated at a temperature of from 35° to 40° C. Under this 

 treatment there was a very considerable range of variation in the 

 stage to which a given period of incubation would bring different 

 eggs ; but there were in one of the two sets of eggs at my disposal 

 no indications of any abnormalities, and there is every reason to 

 believe that the temperature employed was about the natural one. 

 The period of incubation of the emu is three months, as contrasted 

 Avith the four weeks of the fowl, and the time which elapses 

 before any one of the principal events of the development takes 

 place in the former is nearly a corresponding multiple of the time 

 which elapses in the case of the chick. 



An average egg of the emu is twenty-one ounces in weight, 

 and measures rather over four inches in length by three and a 

 half in breadth. Of these about forty may be laid in a season ; 

 when about fifteen have been laid the male bird proceeds to 

 incubate them, and perseveres in this duty until the first set of 

 young ones are hatched, when he is succeeded by the female bird, 

 whicli has now for some time ceased laying. 



• See particularly Dr. C. O. Whitman's admirable "Methods of 

 Research in Comparative Anatomy and Embryology," and the introductory 

 part of the memoir by Duval, quoted below (XII.). 



