FORMATION OF STAPEDIAL PLATE 89 



meantime there have arisen three pairs of bilaterally symmetri- 

 cal sensory epithelia — those of the nostrils, eyes, and ears. 

 Each of these sensory epithelia becomes more or less completely 

 surrounded by a prechondral cytoblastema which subsequently 

 becomes cartilaginous. So striking is the intimacy with which 

 each cartilaginous capsule adjusts itself to the contour of its 

 respective epithelium, that it seems not unreasonable to suppose 

 that each ej^ithelium in some way furnishes the stimulus which 

 effects the chondrification of the surrounding mesenchyme. If 

 this inference be correct, it is evident that the removal of a 

 given sensory epithelium would inhibit the development of the 

 corresponding cartilage. If this also be true, the early removal 

 of the auditory epithelium would furnish a means of testing to 

 what extent the stapes homologue together with its stapedial 

 plate can develop in the absence of a cartilaginous otic capsule, 

 or in the absence of the stimulus to which the latter owes its 

 formation. 



The work of W. H. Lewis ('04) is of great interest and im- 

 portance in this connection. Lewis found that if the otocyst of 

 an anuran be transplanted to the mesenchyme of a urodele, 

 there develops around the transplanted otocyst a cartilaginous 

 capsule which is typically urodelan in character. Unfortunately, 

 experimentation of this sort is at present impossible so far as 

 mammalian development is concerned. Avian development 

 does, however, lend itself to this sort of procedure. 



REMOVAL OF THE OTOCYST 



Chick embryos of from thirty-five to sixty hours constituted 

 the material for experiment. The experiments were of two 

 types: 1) one of the otocysts was coinpletely or incompletely 

 removed by insertion into it of a very warm fine-pointed plati- 

 num needle, for a sufficient length of time to coagulate the 

 liquid contents of the otocyst, whereupon the sensory epithelium 

 would adhere to the needle when it was removed ; 2) the otocyst 

 was transplanted. 



After being subjected to this sort of treatment the eggs were 

 sealed and allowed to incubate for various lengtlis of time— 



