INTRODUCTION 



The origin of the vitreous body of the eye has long been in doubt. 

 Even the numerous and thorough investigations of the first decade 

 of the present century, although clearing up many difficulties and 

 correcting false notions, have failed to bring a satisfactory answer 

 to the question, "Is the vitreous body of the eye a derivative of the 

 outer or middle germ layer ; is it an ectodermal or mesodermal for- 

 mation?" A glance at some of the latest and most widely used 

 textbooks, chosen at random, reveals the uncertainty existing among 

 modern authors as to the origin of this interesting structure of the 

 eye. Says Parker (page 113), "Mesoderm also makes its way into 

 the optic cup, through the choroid fissure, and becomes the vitreous 

 humour." Lillie, on the other hand, maintains (page 275) the 

 "researches of the last few years have demonstrated that the vitre- 

 ous body is primarily of ectodermal origin, its fibers arising as pro- 

 cesses of cells of the inner layer of the optic cup and the matrix 

 as secretion." Again, Prentiss and Arey assert (page 381) that 

 "the vitreous body may be regarded as a derivative both of the 

 ectoderm and the mesoderm. ' ' 



The reasons for this diversity of opinion among biologists may be 

 reduced to the following : 1. The very delicate nature of the vitre- 

 ous body, which differs so widely from all other tissues, renders its 

 study extremely difBcult. It requires special methods of technique 

 not ordinarily employed in histological investigations. The diffi- 

 culties of obtaining perfect sections of the eye in all its stages of 

 development have been regarded by some investigators as almost 

 insurmountable ; 2. The extreme complexity of the mammalian eye, 

 its very rapid development, especially in early embryonic life, the 

 appearance and disappearance of an intricate vascular system in the 

 course of development with its concomitant radical changes — all 

 this obscures the origin and growth of the vitreous body and renders 

 its study as difficult as it is interesting. The vast changes, which 

 follow one another in rapid succession, make it wellnigh impossible 



Contribution from the Biological Laboratory of the Catholic University of 

 America, No. 4. 



