a.uthor'8 abstract of this paper issued 

 by the bibliographic service, march 27 



THE ORIGIN OF BILATERAL SYMMETRY IN THE 



EMBRYO OF CRYPTOBRANCHUS 



ALLEGHENIENSIS 



BERTRMI G. SMITH 



Department of Anatomy, New York University and Bellevue Hospital Medical 



College 



THIRTY-THREE FIGURES 



CONTENTS 



Analysis of the problem 358 



Experiments and observations 360 



A. The possible influence of gravity upon the direction of the median plane 361 



B. The entrance-path of the spermatozoon 362 



1. Relation to the plane of first cleavage 365 



2. Relation to the median plane of the gastrula 365 



C. The relation of the first cleavage furrow to the median plane of the 



gastrula 367 



1 . Orientation experiments 367 



2 . Constriction with a silk thread 368 



3. Staining experiments 370 



4. Direct comparison 373 



5. Instability of the micromeres 374 



D. The excentricity in the superficial cleavage pattern of the early blastula 374 



1. Relation to the median plane of the gastrula 376 



2. Relation to the first cleavage furrow 377 



3. Relation to the entrance-path of the spermatozoon 379 



E. The excentricity manifested by the internal structure of the early 



blastula 379 



1. Relation to the excentricity in the superficial cleavage pattern 382 



2. Relation to the plane of first cleavage 383 



F. The bilateral symmetry of the superficial cleavage pattern in the lower 



hemisphere of the late blastula 383 



1. Relation to the median plane of the gastrula 384 



2. Relation to the first cleavage furrow 385 



G. The bilateral symmetry manifested by the internal structure of the 



late blastula 386 



1. Relation to the bilateral symmetry of the superficial cleavage 

 pattern 388 



2. Relation to the bilateral symmetry of the early gastrula 388 



357 



