584 ON THE EARLY STAGES IN THE DEVELOPMENT OF THE EMU, 



primitive streak region is more readily traceable in the emu, and 

 that the relations of the primitive streak are not complicated by 

 the formation of a sickle or of a sickle-groove. The eai'liest stages in 

 the development of the blastoderm I assume to be similar to those of 

 the embiyos of carinate birds as described by Duval.* Fig. I 



represents a blastoderm of a stage in which the continuity of 

 upper and lower layers (represented by the thickened line 6^)^has 

 become restricted to the posterior border. Fig. 2 repi'esents 

 dia grammatically the infolding of this border by reason of the 



XII. p. 100, &c. 



