300 LEIGH HOADI.KY. 



close histological examination. In normal development, the 

 cartilaginous otic capsule surrounds the sacculus, utriculus, and 

 their derivatives, while the ductus and the saccus endolymphaticus 

 are free in the mesenchyme. The histological differentiation of 

 the several parts of the membranous labyrinth in the grafts is 

 essentially the same as that of the control so that identification 

 can be made positively by histological structure; this is supple- 

 mented as stated above by the general morphological relation- 

 ships present. 



The differentiation attained by the grafted tissues is of two 

 kinds, cartilaginous and epithelial. Xo ganglion cells or other 

 nervous tissue of any kind can be found in the grafts. This fact 

 emphasizes the isolation of the primordium before its transplan- 

 tation, for the ganglion and the otocyst are very closely associated 

 at that early stage. The cartilage partially surrounds the epithe- 

 lium, the latter forming the lining of cavities of various sizes. 

 The relationships of the various parts of the organ is not normal. 

 I have selected for description two cases which show quite an 

 extensive specific differentiation of the membranous labyrinth. 



Graft 32 A 5 is a growth obtained from the transplantation of a 

 forty-eight hour primordium which has remained in the host 

 membrane for six days, a total of eight days growth. Completely 

 surrounding a large epithelial sac is a capsule of cartilage which 

 is discontinuous in two places. Through one gap, small blood 

 vessels enter a narrow group of mesenchymal cells which separate 

 the epithelium of this region from the cartilage surrounding it. 

 The other break in the cartilage sheath is in a place Avhere an 

 incompletely incorporated portion of the epithelium makes a 

 connection with the epithelial sac mentioned above. The car- 

 tilage, from its general relations, is undoubtably the otic capsule. 



The epithelium of the membranous labyrinth shows a high 

 degree of specificity in its mode of differentiation. It may be 

 divided into two main parts, that incompletely incorporated and 

 outside of the cartilaginous capsule, and that within the capsule. 

 The epithelium which is outside of the cartilage is histologicullv 

 identical with that of the normal saccus endolymphaticus, the 

 part connecting the saccus endolymphaticus with the epithelium 

 of the capsule, the ductus endolymphaticus. These two portions 



