Independent Development of the Lens. 419 
emphatically proven that the optic vesicle or optic cup has the 
power without exception to cause a lens to form from the ecto- 
derm with which it comes in contact, even though this ectoderm 
may be far distant from the usual lens-forming area. There is 
probably no strictly limited region of ectoderm from which the 
optic vesicle must stimulate lens-formation. The self-originating 
lenses, however, have invariably occurred in the head region, 
though not always in their usual’ lateral positions. It would, 
therefore, seem that the ectoderm of the head is more predis- 
posed to the formation of lenses than that of the other body 
regions. 
6 SUMMARY AND CONCLUSIONS 
1 When the developing eggs of Fundulus heteroclitus are 
subjected to the action of Mg salts, aleohol, or other anesthetic 
agents, the normal outgrowth of the optic vesicles is generally 
inhibited. Embrvos are obtained either entirely without optic 
cups, with small deeply buried eyes, with only a single eye on one 
side of the head or, finally, with a median more or less double 
cyclopean eye. These specimens furnish exceptional material 
for a study of the relationship between the development of the 
optic vesicle and the optic lens. The embryos with the nervous 
eye parts entirely lacking are similar to specimens with the optic 
vesicles mechanically cut out of the brain. At the same time, 
the injury to the ectoderm which usually results from the opera- 
tion is avoided, and this is a most important advantage. When 
Spemann (’07) operated on Rana esculenta embryos with open 
medullary plates he was able to remove the optic vesicle areas 
from the future inner side of the tube without injuring the ecto- 
derm of the lens-forming region and in such cases independent 
lenses arose on the eyeless side. King (’05) obtained free lenses in 
a somewhat similar experiment. Lewis’ embryos might possibly 
respond in a like manner if operated upon in this fashion. The 
optic vesicle may stimulate a lens from slightly injured ectoderm, 
but the free origin of lenses is a more delicate process and one more 
easily interfered with. 
