25 



the primitive, and the essential portions of the secondary vitreous 

 body, are a purely ectodermal derivative. 



CONCLUSIONS 



1. The vitreous body in its origin is a purely ectodermal struc- 

 ture and consists of delicate fibers, the protoplasmic outgrowths of 

 the basal cells of the retina. 



2. With the development of ,the hyaloid vascular system and 

 the accession of other mesodermal elements, an intimate union 

 arises between the vitreous body fibers and the mesoderm, so that 

 the vitreous body at that stage of development must be regarded as 

 a tissue of derivatives of both the outer and the middle germ layer. 



3. The union between the vitreous body and the mesoderm does 

 not destroy the dependence of the vitreous fibers upon the retina, 

 which during the entire embryonic life controls the development of 

 the vitreous body. 



4. The union of the vitreous body and the mesoderm is not 

 permanent. It is dissolved with the gradual resorption of the hya- 

 loid vascular system and the disintegration of the remaining meso- 

 dermal elements. 



5. The vitreous body in its final development is again a purely 

 ectodermal structure, consisting of great masses of delicate fibers, 

 which have their origin in the basal cells of the ciliary portion of 

 the retina. 



6. There is no hyaloid membrane distinct from the internal lim- 

 iting membrane of the retina. 



7. The hyaloid canal, or rather the hyaloid portion of the vitre- 

 ous body, is found in all advanced stages of development and in the 

 eye of the adult animal. 



8. The hyaloid canal is formed by a thick, membranelike mass 

 of vitreous fibers and contains a loosely arranged fibrous tissue, 

 which may be regarded as the remnant of the secondary vitreous 

 body. 



