POSTURE OF MEMBRANOUS LABYRINTH 171 



the deeper layer of the epidermis. This is the same stage used by 

 me. However, in the technique of the operation our methods are 

 different. Spemann raises a relatively large quadrilateral flap 

 of skin, thereby exposing the ear vesicle, which he loosens and 

 inverts so that the anlage of the ductus endolymphaticus points 

 downward. He then replaces the skin flap and secures it in 

 position by a weight, consisting of a slightly curved strip of cover 

 glass. There are two factors here that may account for the differ- 

 ence in our results. In the first place Spemann, by reflecting a 

 large skin flap, exposes a larger area of the deeper structures and 

 perhaps thereby injures the environment in a way that lessens 

 the postural interaction between it and the ear vesicle. It will 

 be remembered in my operations there was only a linear slit 

 opened, which by the spreading of its edges was sufficient for the 

 manipulation of the vesicle. In the second place the use of the 

 weight, as is done by Spemann, to hold the skin flap in apposition 

 maj^ retard the movement of the vesicle and prevent its rotation. 

 From the nature of my wound no weight was necessary. 



In addition it may be mentioned that Spemann always placed 

 his vesicles so that the median or convex side remained toward 

 the brain, while in most of my experiments it was made to point 

 lateral ward toward the skin. In this respect the displacement of 

 the ear vesicle in my cases was more extreme than in Spemann's, 

 making it all the more difficult for my vesicles to obtain a normal 

 posture. Furthermore, in Spemann's experiments the ear vesicles 

 were replaced in their own original pocket, while in all of my last 

 series they were transplanted to another specimen, here again 

 adding to the difficulty of their postural adjustment. In all 

 other respects there seems to be no essential difference in our 

 methods. 



Judging from my own experiments there certainly exists a de- 

 cided tendency between the ear vesicle and its environment that 

 serves to control the posture, though we know from Spemann's 

 experience that imder certain circumstances this tendency is 

 interfered with and the necessary corrective rotation is not 

 accomplished. 



