Independent Development of the Lens. 421 
9 The optic lens may be looked upon as a once independent 
organ (possibly sensory or perhaps an organ for focusing light on 
the brain wall, before the vertebrate eye had arisen) which 
has become so closely associated with the nervous elements of 
the eye that it has to some extent lost its tendency to arise inde- 
pendently, although still capable of doing so under certain con- 
ditions. The lens now arises much more readily in response to a 
stimulus from the optic vesicle, a correlated adjustment which 
insures the almost perfect normal accord between the optic cup 
and the lens. In experiments on the origin of the lens one must 
guard against disturbing the ectoderm from which an independent 
lens might arise. Although an optic vesicle might have the power 
to stimulate a lens from injured ectoderm, the innate tendency of 
the ectoderm to form a lens is a more delicate impulse and may be 
suppressed by a slight injury or disturbance of the ectoderm 
during the operation. 
7 BIBLIOGRAPHY 
BarrurtH, D. Versuche iiber Regenerationdes Auges und der Linse beim Hiihner= 
1902 embryo. Verh. d. Anat. Gesellsch. Halle. 
Couucci, V.S., Rigenerazione parziale del!’occhio nei Tritoni. Mem. Accad. Se. 
1891 Bologna, Series 5, Vol. i. 
ErGgeNMANN, C. H. The History of the Lens in Amblyopsis. Proc. Indiana 
1901 Acad. Se., 1901. 
FiscHEL, A. Weitere Mitteilungen iiber die Regeneration der Linse. Arch. f. 
1902 Entw’Mech., Bd. xv. 
GemmiLL, J. F. Notes on Supernumerary Eyes, and Local Deficiency and Re- 
1906 duplication of the Notocord in Trout Embryos. Proc. Zodl. Soc. 
London, Vol. i. 
Hersst, C. Formative Reize in der thierischen Ontogenese. Hin Beitrag zum 
1901 Verstiindniss der thierischen Embryonalentwicklung. Leipzig, 
H. Georgi. . 
Kine, H.D. Experimental Studies on the Eye of the Frog. Arch. f. Entw’ Mech., 
1905 XX: 
LeCron, W. L. Experiments on the Origin and Differentiation of the Lens in 
1907 Amblystoma. Am. Jour. Anat., Vi. 
Lewis, W. H. Experimental Studies on the Development of the Eye in Am- 
1904 phibia. I. On the Origin of the Lens. Rana palustris. Am. 
Jour. Anat., ili. 
1907 Experimental Studies, etc. iii. On the Origin and Differentiation of 
the Lens. Am Jour. Anat., vi. 
Accepted by the Wistar Institute of Anatomy and Biology January 12, 1910. Printed June 21, 1910. 
