to forecast with any degree of certainty later developments. The 

 study of the entire embryonic history of the eye alone can solve the 

 mysteries of the origin, the development, and the structure of the 

 vitreous body. It goes without saying that the study of the fully 

 developed eye does not throw much light upon the origin and de- 

 velopment of its parts. 



To attempt a solution of the problem by methods not heretofore 

 employed in this matter, is the purpose of this work. If further 

 justification for reopening the discussion were needed, we might 

 point to the not very creditable fact that, to our knowledge, no 

 special treatise on this subject exists in the English language. 



It was at first planned to make this study comparative, but a 

 closer acquaintance with the work already done made it appear more 

 advisable to investigate the development of the vitreous body of one 

 species from the earliest beginning to its adult condition. The 

 species that was finally selected is the pig, principally on account of 

 the facility of obtaining a complete series of embryonic eyes. More 

 than one hundred and fifty specimens, representing all stages of 

 development, were examined. The material was obtained from the 

 local abattoir. A few specimens were given me by my former 

 teacher, Dr. Carl R. Moore, of the University of Chicago, to whom 

 I extend here my sincere thanks for his interest in the success of 

 this work. Acknowledgment of indebtedness is also made to Pro- 

 fessor J. B. Parker, Ph. D., and Mr. G. J. Brilmyer, M. S., of the 

 Catholic University of America, under whose guidance these investi- 

 gations were made; to Fr. Mahan, S. J., and Dr. T. T. Job, of Loyola 

 Medical School, Chicago, who kindly permitted me the use of their 

 laboratory in the summer of 1920, and to Fr. Victor Herrinjr. 

 0. F. M., for preparing most of the sketches. 



HISTORICAL SKETCH 



The history of the origin of the vitreous body of the eye dates 

 back to the year 1848, when H. Scholer submitted to the University 

 of Dorpat an inaugural dissertation embodying his observations on 

 the development of the chick's eye. Scholer was the first to notice 

 that very early in the development of the chick a very delicate 

 tissue of mesoderm, pars systematis cutis, enters the optic cup 

 through the choroid fissure. Finding no other elements present, 

 Scholer naturally attributed to this portion of the middle germ 



