152 GEORGE L. STREETER 



my papers (Streeter '06 and '07) in which I reported the experi- 

 ments in which, after various displacements, the labyrinths all 

 recovered their normal postural relations, Spemann ('10) made 

 further experiments and reported more at length with regard to 

 postural development. His results confirmed his earlier obser- 

 vations, and his paper contained illustrations showing sections 

 of larvae of different ages in which the inverted ear vesicle has 

 remained inverted though otherwise practically normal. Out of 

 twelve operations nine labyrinths remained inverted, two re- 

 covered partly, and one recovered perfectly the normal position. 

 Regarding the latter specimen he surmised that it had not been 

 sufficiently turned, and had slipped back into its normal position. 

 The results, therefore, as obtained by Spemann are directly con- 

 tradictory to those obtained by me. On account of the great 

 embryological significance of the question of environmental pos- 

 tural control, further experiments were plainly warranted both 

 for the purpose of testing my own previous results and if pos- 

 sible for finding some explanation of the discrepancy existing be- 

 tween the observations of Spemann and myself. From the study 

 of these new experiments and from an examination of the accom- 

 panying photographs it will be plainly apparent that they confirm 

 my previous results. Before entering into a further discussion 

 of them we may proceed with a description of the details of the 

 experiments themselves. 



METHOD OF OPERATION 



Obviously the conditions of the operation should be planned so 

 that the environmental control would be put to an extreme test. 

 In most of my previous experiments, and in all of Spemann's, the 

 vesicle operated upon, after being taken out and rotated one way 

 or another, was replaced in its own pocket. Recovery of the 

 original posture after such an operation might be explained by the 

 possibility of the vesicle not having been completely detached; 

 some small strand of tissue might suffice to draw it back into the 

 original position. Also it is conceivable that, since the vesicle 

 and any adherent mesodermal fragment exactly fitted the pocket 



