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TtiE AMERICAN NATURALIST [Vol. XLII 



occasional in occurrence and locality to justify this. We do not 

 know but that all aquatic cases would have metamorphosed under 

 suitable conditions, and the terrestrial form is indicated as 

 being definitive by the anatomy of the circulatory and respira- 

 tory apparatus. Also we do not share Powers 's objection to 

 the name axolotl and siredon as a designation for the aquatic 

 form; both have the sanction of general usage and do not apply 

 to other animals, so that they are entirely clear. 



H. L. 0. 



EX PER 1 M EXTAL ZOOLOGY 

 Some Experiments on the Development and Regeneration of the 

 Eye and the Nasal Organ in Frog Embryos. 1 — Dr. E. T. Bell has 



conducted a series of experiments on embryos of liana esculenta 

 and It. fusca, in which he found certain new facts in the develop- 

 ment of the eye and nasal organ. Wolff had shown in 1894 that 

 the crystalline lens of the salamander may be regenerated from 

 the upper margin of the iris. Fischel also found later that 

 the lens in the newt's eye would regenerate from the iris, and 

 by wounding the iris in several places after removal of the 

 original lens that one or more lenses were formed. Spemann, 

 Lewis and others show in amphibian embryos that there is no 

 localization of lens-forming material in any given area of the 

 ectoderm, and that the formation of a crystalline lens depends 

 directly upon the stimulation of the ectoderm, or outer embry- 

 onic wall, through contact with the optic-cup. Lewis in a series 

 of interesting experiments in which he tranferred the optic-cup 

 from its original connection with the brain to a more caudal 

 position showed that when it came in contact with the ecto- 

 derm in this new region the optic-cup stimulated lens formation. 

 In another instance the skin from the ventral surface of Rana 

 sylvatica was placed over the optic-cup of //. palusfris and gave 



Bell has discovered several other possible sources of origin 



embryo and turned it completely around so that the former 

 outer side now turned toward the brain ; under these conditions 

 the pigment layer of the retina itself was induced to form a 

 lens-like structure. When the brain was opened in the mid- 



1 Archiv fiir EnUricklungsmccJiamk der Organiamen, XXITI, pp. 457-478, 

 pi. 14 to 20. 



