15 



body fibers and mesodermal endothelial cells, maintains that the 

 retinal fibers aftef entering into a union with the mesoderm, lose 

 all connection with their mother cells of the retina, and become 

 structurally as well as functionally dependent on the endothelium 

 of the blood vessels. We should thus have the unique case of an 

 ectodermal structure separating from its parental tissue and etiter- 

 ing into functional dependence on a mesodermal structure, a phe- 

 nomenon unparalleled in embryonic development. While it is true, 

 that in the inner portions of the optic cup, with progressive differ- 

 entiation, the retina loses the faculty of producing vitreous fibers, 

 this does not hold of the retina in its whole extent. In embryos of 

 25 and even 35 mm length, which marks the height of development 

 of the vascular system, the greater part of the vitreous fibers is still 

 in connection with the retina, while throughout the whole course 

 of embryonic development, and even in the fully developed eye, 

 the vitreous body fibers remain united with the retina in the region 

 of the pars ciliaris sive coeca retince. There the vitreous body never 

 separates from the basal cells of the retina to which it owes its ori- 

 gin. This may be readily seen by comparing the corresponding 

 sections of the eyes of embryos of 25, 35, 60, 80, 100, 130, 175, and 

 250 mm length. As the study of this part of the retina, at various 

 stages of development, throws much light on the development and 

 the ultimate structure of the vitreous body, we have reproduced a 

 number of these both by sketches and by photographs. A 

 close study of these also refutes the theory of v. Lenhossek that the 

 vitreous body, separating from its place of origin, the basal cells of 

 the crystalline lens, forms a, syncytium, deprived of cellular ele- 

 ments, and capable of independent growth, development, and nutri- 

 tion. Even in those regions where the retina loses the faculty of 

 producing vitreous fibers, there is no clear separation between the 

 two. The vitreous body even there retaiiis its intimate connection 

 with the internal limiting membrane of the retina by a great number 

 of very delicate fibrils, which form the ragged edge of the vitreous 

 body in sections where shrinkage has pulled the two apart. 



That the vitreous body fibers also enter into close relationship 

 with the free mesodermal elements found in the vitreous body is 

 made clear by many sections. After the manner of embryonic con- 

 nective tissue cells, many of the mesoderm cells assume a stellate 

 or fusiform shape and send out protoplasmic processes of greater or 

 shorter length. From these not infrequently long slender threads 



