16 



arise which attach themselves to any structure within reach, whether 

 other mesoderm cells or blood vessels or vitreous body fibers. There 

 seems to be no doubt that the latter also enter into direct union with 

 the mesoderm cells. We have thus an extremely complex relation- 

 ship between retinal fibers, blood vessels and free mesoderm cells. 

 We would emphasize this fact in view of the contention of Mavas, 

 Magitot, and Seefelder, that the mesodermal elements present in the 

 vitreous body are hermetically shut off (Seefelder) from the latter, 

 thus excluding the possibility of mesodermal contributions to the 

 vitreous body. 



In view of the complex relationship between ectodermal and 

 mesodermal elements in the vitreous body, we agree with v. Szily 

 that the "vitreous body problem" is not so much to decide its ori- 

 gin, which at the present time is almost universally regarded as 

 ectodermal, but to determine the influence of various mesodermal 

 structures upon its further development. Szily puts the question 

 on a wider basis in so far as he maintains the real point at issue is 

 the union of two structures, primarily derived from different germ 

 layers, into one tissue. While all our preparations of many stages 

 of development of the eye of the pig, reveal this complex union 

 of mesodermal and ectodermal derivatives in a clear and unmis- 

 takable manner, we are not prepared to follow v. Szily in asserting 

 that the ectodermal vitreous body fibers become also functionally 

 dependent on the mesoderm. It is the retina which gives rise to the 

 primitive vitreous body ; it is the retina which directs and controls 

 the development of its structural parts; it is the retijut which in the 

 fully developed eye contributes exclusively to the formation of the 

 vitreous body. The retina alone never loses its original relationship 

 to the vitreous fibers; upon the retina they are structurally and 

 functionally dependent in their origin, developraent, and final ar- 

 rangement. Though this intimate relationship between retina and 

 viti'eous body is found at first in the whole extent of the retina, it is, 

 however, later restricted to a narrow circular strip of the retina 

 between the ora serrata and the pars cUiaris retiiuf proper. There 

 the controlling influence of the retina upon the vitreous body fibers 

 is manifest at every stage of development as well as in the eye of 

 the adult animal. 



Our conception of the relationship between retina and vitreous 

 body finds a singular confirmation in the results of experiments 

 made by Haemers to determine whether regeneration of the vitreous 



