17 



body is possible and how it takes place. After a number of experi- 

 merits on the eyes of various animals, Haemers asserts that "the 

 vitreous body regenerates at the expense of the retinal neuroglia" 

 (page 114) ■ But surely, the regeneration of one tissue from another 

 presupposes a relationship of dependence between them. It is to 

 be regretted that Haemers has not found any followers in his in- 

 genious attack upon the vitreous body problem by a careful study of 

 the process of regeneration. No doubt, a repetition and extension of 

 Haemers' investigations would tend to clear up other difSeulties 

 and point the way for a final solution of this interesting and difficult 

 problem. Regeneration of the vitreous body has been observed also 

 by Sauri. 



During the period of development described in this chapter, 

 the general appearance of the vitreous body has greatly changed 

 even in the regions not directly affected by the invasion of the meso- 

 derm. While during the earlier stages, including embryos of 35 mm 

 length, the radial fibers still form the larger part of its structure, 

 we soon observe that they are more and more replaced by fibers run- 

 ning approximately parallel to retina and lens. The parallel fibers 

 are at first found in the exterior regions of the vitreous body near 

 the retina, where they gradually assume the appearance of a special 

 membrane, distinct from the internal limiting membrane of the 

 retina, and forming the outer covering of the vitreous body. It has 

 been generally called the hyaloid membrane. Later a number of 

 fibers are found to take their course from the region anterior to the 

 ora serrata to the posterior part of the lens and then turn inward 

 in the direction of the optic nerve. They represent the first traces 

 of a more solid portion of the anterior surface of the vitreous body, 

 and they have sometimes been called the anterior hyaloid membrane. 

 The discussion of the significance of these structures will be reserved 

 for the next chapter. 



Our conclusions, derived from the study of this most important 

 period in the development of the vitreous body, may be summed up 

 thus: The original purely ectodermal structure of the vitreous 

 body is radically changed by the accession of various mesodermal 

 elements in the form of blood vessels and free mesoderm cells with 

 their outgrowths. The ectodermal vitreous fibers enter into a close 

 relationship with the mesoderm, the relationship being one not only 

 of contiguity but of protoplasmic continuity, consisting of a pro- 

 toplasmic union between them. This union, however, does not de- 



