8 



placode (Figure 6), and in which at this time no mesoderm has 

 entered through the choroid fissure (Figure 1), it would be difficult 

 to account for the presence of mesoderm in the vitreous body. 

 In structure, the cells resemble the retinal cells. For these 

 reasons, we incline to the belief, that they are of retinal origin and 

 not mesenchyme. But whatever their origin and their nature may 

 be, they show no connection with the vitreous body, nor do they at 

 this stage of development contribute to the production of the vitre- 

 ous fibers. 



The vitreous body is represented in all embryos by a great mass 

 of fibers, of which the larger portion extend radially between the 

 retina and the lens, while, especially in embryos of 10 and 11 mm, 

 some very prominent fibers are seen running approximately parallel 

 to the retina and lens. It is not difficult to determine the origin of 

 both. The radial fibers arise as long slender outgrowths from the 

 conelike bases of the inner layer of retinal cells (Miiller's support- 

 ing cells). Some can be traced directly from the retina to the lens, 

 others are seen to send off branches in various directions which, 

 dividing and subdividing, anastomose freely with branches from 

 neighboring fibers, forming a dense reticulum in which further 

 tracing becomes impossible. The fibers are slightly granular and 

 react to the various stains in a manner not unlike that of the 

 cytoplasm of their mother cells. In some sections, larger granules 

 are found at the junction or branching points of the fibers, but their 

 absence in the more perfect preparations, especially in the celloidin 

 preparations, seems to show them to be artefacts, produced by 

 precipitation. In the more perfect sections, the fibers appear almost 

 homogeneous, slightly granular, tapering gradually from their 

 broad bases at the retina to a slender thread near the lens. In the 

 narrow isthmus between the anterior part of the retina and the 

 lens, a very regular structure of the fibers is frequently found. 



The radial fibers, however, are not restricted to the retina; the 

 basal cells of the lens also send out a large number of them. These 

 fibers differ widely from the retinal fibers. They are short and 

 never traceable to the retina. At a short distance from the lens, 

 they split into several branches which run almost parallel to the 

 posterior part of the lens. At this point they are met by the more 

 numerous and more massive retinal fibers, and together with them 

 they form a thick, feltlike mass, especially observable in equatorial 

 sections (Figures 1 and 8). The entire surface of the lens con- 



