GROWTH OF THE INNER EAR OF ALBINO RAT 145 



4. Within the cochlea the cell bodies and nuclei increase 

 their diameters from the base toward the apex, except in the 

 earlier stages. 



5. There are no evident differences in the diameters of the 

 cell bodies and the nuclei of the ganglion cells either according 

 to sex or side. 



6. Both the cell bodies and the nuclei are immature at birth, 

 but differentiate rapidly, and even at six days the Nissl bodies 

 are visible. The differentiation proceeds with advancing age. 



7. The ganglion cells are bipolar and oval in shape. The 

 direction of the long axis of the cells differs according to the 

 turn of the cochlea and in the upper turn it runs almost parallel 

 to the axis of the modiolus but inclines more and more to the 

 horizontal position on passing to the base. 



8. The nucleus-plasma ratios of the ganglion cells increase 

 with age in both the radial and cross-sections. 



9. The increase in the volume of the ganglion cells and the 

 area of the cross-section of the hair cells is approximately sim- 

 ilar during the first nine days of life, but after that the ganglion 

 cells increase relatively very rapidly. These relations are very 

 different from those found for the spinal ganglion cells by Don- 

 aldson and Nagasaka ('18) and for the cells of the gasserian 

 ganglion by Nittono ('20). 



The nervus cochlearis innervates not only the hair cells, but 

 all the elements of the cochlea, and this may have some in- 

 fluence upon this relation. It is interesting to note that the 

 rate of increase in the cylindrical surface of the hah* cells is 

 similar to that in the area of the cross-sections of these same 

 cells. 



II. CORRELATION BETWEEN THE INCEPTION OF HEARING 

 AND THE GROWTH OF THE COCHLEA 



The present study aims merely to compare in the rat the 

 size of each element of the cochlea just before and just after 

 the appearance of hearing and to ascertain the changes in the 

 cochlea which take place during this phase. The rats which 

 have sense of hearing show the so-called ' Ohrmuschelreflex ' 



