left for an additional two to four days. Without being washed, 

 they were then transferred to concentrated acetone for two to three 

 days. To facilitate dehydration, a layer of calcium chloride was 

 spread in the bottom of the vessel. To prevent a too violent action 

 of the calcium chloride on the eyes, direct contact between the two 

 must be avoided. The material was then placed for twenty-four 

 hours in ether-alcohol, and thereafter embedded. Embedding was 

 done in celloidin or paralodion, dissolved in ether-alcohol, smaller 

 eyes being placed successively in 2, 5, 8, and 10% solution, larger 

 eyes in 1, 3, 5, and 8% solution, remaining in each about three days. 

 Parts of the coats of the eyes were removed before embedding to 

 insure perfect penetration. Hardening was done by means of 

 chloroform and terpineol. Sections were cut very thick, 100, 150, 

 200, 250, and 300 microns. They were placed into a 95% alcoholic 

 solution of iodin to remove the mercuric chloride crystals, then into 

 75% alcohol and, immediately before staining, into distilled water. 

 Various stains were tried, the best results being obtained with 

 Held's molybdic haematoxylin (haematox. cryst. 1 g., molybdic 

 acid 10 g., 70% alcohol 100 cc). The stain was permitted to ripen 

 about three weeks, carefully decanted and, before use, diluted with 

 ten times its volume of distilled water. The sections were then 

 passed through the various grades of alcohol to 95%, cleared in 

 carbol-xylol, and mounted in balsam. The structure and arrange- 

 ment of the fibrous part of the vitreous body were brought out with 

 remarkable clearness in this way, but, unfortunately, the remain- 

 ing structures were deeply overstained. To remedy this defect, 

 some sections were stained in Lyons Blue, but with indifferent 

 success. 



INVESTIGATION 



I PEiMiTrra Vitreous Body 



The period of development forming the object of this part of 

 our investigation, includes embryos ranging from 4 to 11 mm in 

 length and shows the origin and growth of the eye from its begin- 

 ning to the completion of the optic cup and the lens vesicle, before 

 the appearance of blood vessels in the cavity of the vitreous body. 

 It shows the latter in its primitive and simplest form, not obscured 

 by the numerous mesodermal elements, which later render its study 

 more difficult. 



