THE EMBRYONIC HISTORY OF THE LENS IN BDELLOS- 
TOMA STOUTI IN RELATION TO RECENT EXPERIMENTS. 
BY 
CHARLES R. STOCKARD. 
Pathological Laboratory, Cornell University Medical College, New York City. 
WitTH 3 TEXT-FIGURES. 
Spemann, Lewis, and others, have shown by experiments on amphibian 
embryos that there is no localization of lens-forming material in any 
given area of the ectoderm, and that the formation of a lens depends 
directly upon the stimulation of the ectoderm by a contact with the 
optic-cup. Spemann* has since discussed the question of the self-differ- 
entiating power of the lens and concluded from a consideration of 
Schaper’s * experiments on the frog that the lens is not self-differentiating, 
but that a durable influence or contact of the optic-cup is necessary 
to cause the lens-plate or lens-bud to develop into a typical lens. Le Cron ° 
has lately shown by a series of convincing experiments that the lens 
in Amblystoma is not self-differentiating. He found when the optic-cup 
was artificially removed from below the lens-plate, lens-bud, or lens- 
vesicle that the lens structure soon ceased to further differentiate and 
commenced to undergo degeneration. In most of these experiments 
the authors have considered the possibility that the injury caused by 
the operation might be responsible for the failure of the lens to form, 
although their methods and care have been sufficient to convince one 
that such was not the case. 
1Spemann, H., Ueber Correlationen in der Entwickelung des Auges. 
Verhandl. der Anat. Gesellsch., 1901. 
2Lewis, W. H., Experimental Studies on the Development of the Eye in 
Amphibia. I. On the Origin of the Lens. Rana palustris. Am. Jour. Anat., 
III, 1904. 
3 Spemann, H., Ueber Linsenbildung nach experimenteller Entfernung der 
primadren Linsenbildungzellen. Ausftihrlich: Zool. Anz., 28, 1905. 
*Schaper, A., Ueber einige Falle atypischer Linsenentwickelung unter 
abnormen Bedingungen. Anat. Anz., XXIV, 1904. 
5 Le Cron, W. L., Experiments on the Origin and Differentiation of the Lens 
in Amblystoma. Am. Jour. Anat., VI, 1907. 
AMERICAN JOURNAL OF ANATOMY.—VOL. VI. 
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