24 THE HISTOGENESIS AND GROWTH OF THE OTIC CAPSULE AND ITS 



sulated by a clear space that varies in size and shape and whose contour seems to 

 be formed by the persisting processes of the original syncytium. At first the 

 nucleus is accompanied by very little condensed protoplasm, but this gradually 

 accumulates after the formation of the encapsulated spaces and constitutes a cell- 

 body of endoplasm. The nuclei continue to divide after the encapsulation and 

 they can be seen in all stages of the process. The space shares in the subdivision 

 and for a time each daughter nucleus inherits its own share of the space. The 

 encapsulated spaces, in an embryo 17 mm. long (Carnegie Collection, No. 576), 

 which had been stained deeply with hematoxylin and eosin, contained a homo- 

 geneous substance that was tinged with eosin. The substance was collected around 

 the nucleus and filled more than half of the space of the capsule ; but clearly it was 

 not protoplasm and was not to be confused with the endoplasmic cell-body which 

 forms later. None of this substance was found in the matirx surrounding the 

 capsules. 



The embryos in the Carnegie Collection that, on account of the stain that was 

 used and the thinness of the sections, show particularly well the process of the 

 differentiation of the encapsulated spaces are as follows: No. 576, 17 mm.; No. 

 409, 16 mm.; No. 296, 17 mm.; No. 409, 18 mm.; No. 455, 24 mm.; and No. 453, 

 23 mm. The order in which they are given indicates their relative development. 

 In all of them areas are found showing different stages in the differentiation. On 

 comparing them one could come equally well to two different conclusions regarding 

 the encapsulation of the nuclei and the differentiation of the matrix. One could 

 either say that the mesenchymal syncytium during the precartilage period under- 

 goes a fusion into a semi-solid, homogeneous, slightly opaque mass in which the 

 fibrils disappear and which forms the precartilaginous matrix, while at the same 

 time selected spaces of the original syncytium develop a sharp margin and become 

 encapsulated, each containing its own nucleus, or, one could say that the substance 

 composing the matrix is deposited in the meshes of the syncytium, replacing most 

 of the fibrils and obliterating the spaces except those selected ones that are inclosed 

 by persistent processes and are encapsulated with an adjoining nucleus. One 

 can not, however, see much evidence for considering the encapsulated spaces as 

 of vacuole formation. They are certainly not vacuoles of the endoplasm, for the 

 endoplasm does not make its appearance until after the spaces have taken on their 

 characteristic form. 



DIFFERENTIATION OF CARTILAGE. 



The transition from precartilage to cartilage is a gradual differentiation that 

 takes place in the otic capsule of embryos between 25 and 30 mm. long. If one 

 examines an embryo 30 mm. long, such as shown in figure 11, it will be seen on com- 

 paring it with younger stages that the main capsular mass has undergone a distinct 

 maturation. Tlii.s transition is marked by a considerable increase in the amount 

 of matrix combined with a more complete encapsulation of the nuclei, or cartilage 

 cells as we may now call them. As the matrix increases in amount it also changes 

 in its chemical composition, so that it is now possible to stain it differentially. 



