FORMATION OF STAPEDIAL PLATE 95 



the region of the small abandoned sensory epithelium and follow 

 its contour very closely. If, for example, a small ventral por- 

 tion of the otocyst be left in the embryo, it will take on the form 

 of a hollow sphere which will generally be found in the region 

 normally occupied by the lower portion of the lagena. The 

 cartilage surrounding it will likewise be found to be a sphere. 

 It may be of interest to state that in chemically treated teleost 

 embryos it sometimes happens that both otocysts fuse more or 

 less completely in the median plane. Whatever may be the 

 configuration of the sensory epithelium, the developing otic 

 capsule always conforms to the shape of the former. It seems 

 well established that the cartilages forining about the three 

 main pairs of sensory epithelia in the head are formed in response 

 to the presence of those epithelia. 



DISPLACEMENT OF THE OTOCYST 



It was found that the otocyst, when displaced into foreign 

 mesenchyme, caused cartilage-formation. It was hoped that 

 both distinct otic capsule and stapedial plate might be induced 

 to form from mesenchyme far removed from the head-region. 

 The results of this sort of experiment are not yet sufficiently 

 clear-cut to warrant their discussion. One case of displacement 

 may, however, be profitably considered, namely, one in which 

 the upper portion of the otocyst was transferred to a region which 

 afterwards proved to be the foramen through which the facial 

 nerve passed. 



The embryo to be described was fifty hours old at the time of 

 operation. A warm needle was introduced into the otocyst, 

 the liquid contents of which became sufficiently coagulated that 

 a pull of the needle was able to move the otocyst in the 

 loose mesenchyme. The needle was pulled outwards and dorso- 

 anteriorly and held in that position as steadily as possible for a 

 considerable time. A small amount of warm Ringer's solution 

 was allowed to run down the needle, drop by drop, until the 

 needle could be pulled out of the coagulum. In this instance 

 the entire otocyst did not follow the needle but pulled asunder, 

 a small portion remaining in its original position; this fragment 



