320 GEORGE W. BARTELMEZ. 



I wish to call particular attention to the older studies on the 

 bird's egg. From the time of Aristotle until the work of Kolliker, 

 O. Hertwig and van Beneden began, the only accredited and 

 accessible embryological material was afforded by the hen's egg 

 and a wealth of observation was accumulated concerning it. 

 Yet recent students of the bird's egg have dated their work 

 from Gegenbaur's paper in 1861 assuming that the monumental 

 researches of Harvey, Malpighi, Wolff, Dutrochet, Coste and 

 even Purkinje and von Baer have now only an historic interest. 

 The folly of this will appear from what follows. These workers, 

 unhampered by our elaborate technical methods, studied this 

 macroscopic egg with the thoroughness of studious leisure and 

 then wrote of it in a manner that must arouse the wonder and 

 admiration of any embryologist today. The neglect which 

 Purkinje has suffered can be explained at least in part, but the 

 oblivion in which v. Baer's work still languishes is incompre- 

 hensible. 



The findings reported here are significant not alone in illuminat- 

 ing the nature and causes of the variability in the relations of the 

 axes of bilaterality. They have also a direct bearing upon all 

 descriptive studies of the earliest stages of the bird's egg and 

 they must especially be taken into account in the interpretation 

 of experimental studies of stages preceding the appearance of 

 the primitive streak. 



In order to discuss the literature it will be necessary to begin 

 with a general statement of our knowledge concerning the axes 

 of the bird's egg, working backwards from the incubated egg to 

 the ovarian oocyte. 



After the appearance of the primitive streak the bird's egg 

 presents two obvious axes of symmetry; one a general axis of 

 the egg as a whole, the principal axis, the other the axis of the 

 embryo itself. Both of these are more or less apparent in other 

 eggs, especially the highly meroblastic eggs of reptiles and 

 selachians, but so far as is known it is only in birds that these 

 two axes are definitely related to one another. The fact that 

 they are related indicates that they are expressions of the same 

 (bilateral) symmetry of the organism a thesis for which I 

 brought forth abundant evidence in 1912. Unfortunately we 



