FORMATION OF STAPEDIAL PLATE 103 



If there exists a necessary nexus between the conditions above 

 described and the deductions which have been made, it may be 

 profitable to emphasize the following points: 



The removal of the otocyst from young chick embryos seems 

 entirely to do away with the stimulus to the later development 

 of the otic capsule. 



Embryos devoid of otic capsules fail to develop stapedial 

 plates. 



If it be objected that the removal of the otocyst produces 

 the apparent inhibition by injury or removal of the mesenchyme 

 surrounding the otocyst, it can only be urged that in case of 

 mere transplantation it is unlikely that there was sufficient heat 

 to injure the outlying mesenchyme when the auditory epithe- 

 lium itself was not seriously injured. If it be objected that such 

 formative mesenchyme was moved bodily in case of complete 

 removal, it might be urged that such displaced mesenchyme 

 failed to produce a stapedial plate in case of displacement of 

 the otocysts. Furthermore, it seems improbable that the in- 

 jury of the mesenchyme at the site of first invagination of the 

 sensory epithelium should affect very profoundly the mesen- 

 chyme lying ventral to the hind brain in the potential region of 

 the extremity of the lagena. 



The columellar portion of the stapes of birds seems to pene- 

 trate the center of the stapedial plate (stapedial 'flange' or sta- 

 pedial 'ring'), so that the central mesial surface of the columella 

 actually forms a portion of the internal surface of the stapedial 

 plate at least in embryos of eight to ten days. The present 

 study has not determined the permanency of these conditions. 



Whether the results here outlined demonstrate the stapedial 

 plate to arise from the otic capsule, they certainly point to a 

 possible kinship of the two structures, in that the same exciting 

 stimulus is a factor in the production of each. The columellar 

 portion of the stapes attains its full length and normal propor- 

 tions in the absence of a stapedial plate; this fact offers a signifi- 

 cant contrast in the nature of the latter structures. The stapes- 

 homologue in birds seems to be of mixed origin, cranial and 

 visceral. 



