Vol. XXXV. December, 1918. No. 6 



BIOLOGICAL BULLETIN 



THE RELATION OF THE EMBRYO TO THE PRINCIPAL 

 AXIS OF SYMMETRY IN THE BIRD'S EGG. 



GEORGE W. BARTELMEZ, 

 FROM THE DEPARTMENT OF ANATOMY, THE UNIVERSITY OF CHICAGO. 



CONTENTS. 



I. The Fundamental Relations of the Various Parts of the Bird's Egg 319 



II. Historical Review 324 



A. The Principal Egg Axis 324 



B. The Air Space 324 



C. The Shell Pigment 333 



D. The Chalazae 325 



E. Ligamentum Albuminis 328 



F. The Long Axis of the Yolk 328 



G. The Oviducal and Ovarian Orientation 334 



H. The Relation of the Embryo to the Principal Egg Axis: Axis 



Angle 335 



III. Axis Angles in the Pigeon's Egg 339 



IV. Discussion 347 



A. Variability in Axis Angles 347 



B. Inversions 349 



C. Variability in the Chalazae 353 



V. Conclusions 355 



Bibliography 356 



While studying the earliest stages in the development of the 

 pigeon's egg some years ago it became necessary to devote some 

 attention to the laid egg. Here I found several relations of 

 fundamental importance which recent embryologists have con- 

 sistently neglected. It was especially interesting to find that 

 the well-known relation between embryo and egg as a whole 

 (Fig. i) is subject to much greater variation than is generally 

 believed. This became still more striking when it was found 

 that the eggs of a single bird vary less than the eggs obtained 

 from a group of birds. The present report covers observations 

 extended over a much longer period than my former one (1912), 

 together with an analysis of the data and the literature. 



319 



