18 CHIKANOSUKE OGAWA 



Spemann ('10) worked independently on a similar problem. 

 He took out the ear cup of Rana esculenta larvae in a very early 

 stage and replaced it in an inverted position on its transverse 

 axis. His conclusions are just the contrary of those of Streeter, 

 as he found that the ear vesicle continued to develop without 

 returning to its original posture. Streeter is inclined to seek an 

 explanation for this discrepancy in a difference in operation 

 methods. The present paper is designed to throw further light 

 on this and certain other related problems: 1) When does postu- 

 ral readjustment of the ear vesicles take place? Do the vesicles 

 slip back, as it were, into their normal position immediately 

 after the operation? Do they rotate before or coincidentally 

 with differentiation of the various structures of the ear? 2) Does 

 such rotation occur also in ear vesicles transplanted from one 

 specimen to another of a different order? 3) What are the 

 results when inversion is made on the transverse axis by Streeter 's 

 method? 



I wish to extend my heartiest thanks to Dr. G. L. Streeter for 

 his constant interest while this work was in progress, and I also 

 take pleasure in acknowledging my indebtedness to him for many 

 valuable suggestions, as well as for the use of his preparations 

 of tadpoles operated upon and preserved at very early stages 

 (from fifteen minutes to five and one-half hours after operation). 



MATERIAL AND METHODS 



For a study of the first and third problems I made use of Rana 

 palustris larvae; for the second, Amblystoma and Rana. In 

 order to prolong the period for operations, I placed the freshly col- 

 lected eggs in a refrigerator, taking them out as needed. The 

 method of operation was that described by Streeter ('14). Two 

 larvae were placed side by side under a binocular microscope. 

 With two embroidery needles an incision was made through 

 the ectoderm of one of the specimens, over the site of the ear vesi- 

 cle. With the needles the vesicle was loosened from its pocket 

 and cast away. The vesicle of the second specimen was un- 

 covered in a similar manner and slipped into the empty pocket 



