CHORIO-ALLAXTOIC GRAFTS. 3OI 



are surrounded by mesenchyme only, as in the control. The 

 parts within the cartilaginous capsule show a high degree of 

 differentiation also. In the region of the vascular foramen refer- 

 red to above, the epithelium has the characteristics of the normal 

 utrirulu- of the ei.^ht day chick embryo. This determination i- 

 further confirmed by the appearance in the epithelium of three 

 thickened which represent the cristae acusticae of theampul- 



lae of raicircular canals. No ganglion cells ai ociated 



with thi in the controls. There are no canals or ampulla- 



forim-d though at a point o.cupied by one of the cristae I ig. 7. 



~< ; 



C-^: 

 ' 



I ic vesicle of forty-*-:. 



lit days growth. 32 AS- (X 23; /' I. 



:ng beginning of can. i Cart '.la^c 



i. . .i|i-i:N. M .chyme containing M I v- 



.'u-liiim. 



Compare Fig. s there is a slight evagination which suj the 



inning i-l" -in h i"rmation. It is very limited in extent, 

 appearing for only a l\-\v sections. Thn 'ii^h the -paci- formed by 

 tin- second break in the cartilage, the 1 C liiu-d b\- utricular 



epithelium i- ronm. led to the endolymph.itic derivatives men- 

 tioned abo\e. A few -ertions be\'ond this the wall of the sac 

 -li>w> a differentiation into ., -tratilied -arcultis-like an<l a thinner 

 utricular epithelium. The ductus cochleari- and the lagena 

 which normally ari-e from the sacculus are absent in the craft. 

 It may \ery well be th.it the presence of the cartilage sheath has 

 arted a- a mechanical obstruction to t heir formation. 



