438 



George L. Streeter, M.D. 



Ing the question of posture. However, in five cases, which will 

 be presently described, where the ear vesicle was transplanted 

 from the left side to the right side into the place made vacant by 

 the removal of the right ear vesicle, in spite of the fact that these 

 ear vesicles were implanted with haphazard attitude toward the 

 adjacent structures, they nevertheless in each instance developed 

 right-side up, and with the median surface toward the brain, as 

 can be seen in Figs. 5 and 6. 



5 ac. e n d ol y ID ph 

 Rhombenceph. 



Mese^nceph. 



Biepce p h, 



Med. spina 



Gang, prooti c. 

 La'qena 



Te 1 e n c € p h 



Fig. 5 Reconstruction showing the form and relations developed by a left ear vesicle when trans- 

 planted to the right side; it shows that under such circumstances the ear vesicle retains its left-sided 

 characteristics, though it otherwise normally adapts itself to its new situation. A photograph of the 

 same specimen is shown in Fig. 6, c. 



DETERMINATION OF THE DEXTRAL AND SINISTRAL CHARACTER 

 OF THE EAR VESICLE 



The question as to whether the right or left-sidedness of the ear 

 labyrinth is controlled by the environment, or is determined by 

 some intrinsic character of its own constituent cells, is answered 

 in favor of the latter by the fact that if the left primitive ear vesicle, 

 before the time of its complete closure, is transplanted to the oppo- 

 site side of the embryo it retains its original left-sidedness. In five 

 specimens, at the usual operating stage, the right ear vesicle was 

 removed, and at the same time the left ear vesicle was uncovered 

 and lifted from its natural bed and then placed into the pocket 



