POSTURE OF MEMBRANOUS LABYRINTH 153 



from which they were taken, they might on that account slip back 

 into their original position. Both of these obj ections were avoided 

 by transplanting a vesicle from one specimen into the emptied ear 

 pocket of another specimen. This certainly involved complete 

 detachment, and it is obvious that the transplanted ear vesicle 

 would not exactly fit in a pocket in which it did not originally 

 belong. All of the following experiments were done in that way. 



The experiments were carried out on larvae of Rana pipiens, and 

 the operating stage was the same as that used in previous experi- 

 ments (Streeter '06, fig. 3, p. 547). This is just at the end of the 

 non-motile stage, and the outer form of the larvae shows a distinct 

 tail bud, and the eminences on the head caused by the optic cup 

 and head ganglia. The ear consists of an invaginated saucer- 

 shaped mass of cells just in the process of being pinched off from 

 the deeper layer of the skin, with the edges inverted and in the 

 process of completing the closure of the vesicle ; that is, transition 

 from auditory cup to auditory vesicle. In this, as in previous 

 papers, the attempt is not made to distinguish between these two 

 stages, and the term 'ear vesicle' is used to cover both. The 

 technique of the operation is as follows : Two larvae are removed 

 from their gelatinous capsules and placed side by side in distilled 

 water, under a binocular microscope. With two no. 12 embroid- 

 ery needles, a linear tranverse incision is made through the ecto- 

 derm of one of the specimens over the site of the ear vesicle, the 

 incision being about three times as long as the vesicle, and the 

 right side of the animal always being used for the operation. The 

 lips of the wound are than gently everted, forward and backward 

 respectively, which discloses the thin lateral wall of the vesicle, 

 or if this is torn in the removal of the skin then one sees the 

 pigmented concave interior of the vesicle. With the needles the 

 vesicle is now loosened from its pocket and cast away. This 

 leaves an empty pocket, free for the transplantation. The right 

 vesicle of the second specimen is uncovered in a similar way, 

 loosened from its pocket and then slipped into the empty right 

 auditory pocket of the first specimen. In tucking in the vesicle 

 under the edges of the wound care was taken in all cases to 

 place the vesicle so that the lateral or concave open surface of 



