4^2 George L. Streeter, M.D. 



normally buds out from the caudal border of the saccule in these 

 cases is found extendmg forward toward the prootic ganglion. 



The ear vesicle, however, is not in all respects independent of 

 the surrounding structures. Some experiments which are reported 

 below, mdicate that its position in reference to the brain, ganglion 

 masses and the surface of the body is determined by the environ- 

 ment Itself; it may be rotated in any direction, and nevertheless it 

 eventually develops in the normal attitude, with the saccule toward 

 the ventral surface, the semicircular canals toward the dorsal 

 surface, the lateral semicircular canal being toward the lateral 

 surface, and the endolymphatic appendage toward the brain. 



The experiments were carried out on larvjie of Rana sylvatica 

 and Rana pipiens, and the operating stage was the same that 

 was used in previous experiments.'^ The time is just at the close 

 of the non-motile stage, and the epithelial ear consists of an invag- 

 inated cup-shaped mass of cells just in the process of being pinched 

 off from the deeper layer of the skin, with the edges turning in to 

 form a closed vesicle. For simplicity the term *'ear vesicle" will 

 be used even though the closure is not yet complete; the attempt 

 to distinguish between auditory cup and auditory vesicle does not 

 seem to be justified for the present purposes. The technique of 

 the operations was also the same as that described in the previous 

 paper. Notes were made on the behavior of the animals, and 

 at the end of from four to six weeks the specimens were preserved 

 in a chrome-acetic mixture, cut in serial sections, and stained with 

 haematoxylin and congo red. With certain specimens the ear 

 vesicle, adjacent ganglia, and a portion of the central nervous sys- 

 tem were reconstructed after the Born wax plate method. Eleven 

 such models were made, and photographs of some of them are 

 reproduced in Figs. 2, 3 and 6. With the aid of these models it 

 was possible to identify relations and detailed features of the laby- 

 rinths that otherwise could not have been recognized. 



The morphological features of the experiments will be first con- 

 sidered, and the behavior of the animals and its relation to equilib- 

 rium will be treated separately in the latter part of the paper. 



' Streeter '06: /. c, Fig. 3, p. 547. 



