490 PATTERNS AND PROBLEMS OF DEVELOPMENT 



dermis for that normally overlying the eye by reversing the anteropos- 

 terior axis of head epidermis, by transplanting epidermis from other re- 

 gions of head or trunk, or by regeneration of epidermis from adjoining 

 regions after removal of the presumptive lens epithelium has also given 

 positive results in many species. ^^ Regenerating tissue of urodele leg and 

 tail and of anuran tadpole tail transplanted to the eye may form a lens 

 after removal of the original lens (Schotte and Hummel, 1939). Even 

 optic vesicles explanted with skin pieces may induce a lens in other than 

 the presumptive lens epidermis (Perri, 1933). 



As the data stand at present, lens can be induced in head epidermis 

 not immediately adjoining the eye region and in trunk epidermis by the 

 optic cup in R. fiisca, R. sylvestris, R. temporaria, R. catesbiana, R. ridi- 

 bunda, R. pipiens, Hyla arborea, in trunk epidermis, probably also in 

 head epidermis but data are lacking, and in T. taeniatus and Pleurodeles 

 waltlii. According to earlier experiment (Spemann, 1912a), lens induction 

 occurred only in head epidermis in Bombinator pachypus and R. esculenta, 

 but more recently it has been obtained from both head and trunk epi- 

 dermis in both species. Earlier experiment on A. pundatum gave posi- 

 tive results only with epidermis adjoining the presumptive lens epidermis, 

 but Stone and Dinnean (see footnote 39 below) report lens induction in 

 ventral ectoderm. 



In general, reactivity appears to be less in trunk than in head epider- 

 mis, particularly in regions near the eye. Lenses induced in trunk epi- 

 dermis are usually smaller and less developed, and apparently less fre- 

 quent, than in head epidermis, suggesting a relation between the effect 

 of induction and position of the epidermis in the anteroposterior gradient. 

 Although nasal and otic primordia of Hynobius are capable of independ- 

 ent differentiation, the optic cup can induce lens in them by overcoming 

 whatever determination exists (Ikeda, 1937). 



Mangold and Spemann regard the data as indicating that in some 

 species — for example, R. esculenta and A. pundatum — the presumptive 

 lens region is determined as lens before the optic cup comes into contact 

 with the epidermis, while in others it is not so determined or is less deter- 

 mined, and that, in general, capacity of other epidermis to react to the 



39 W. H. Lewis, 1904, 1907a, b; Spemann, 1905, igiia; Ekman, 1914; Harrison, 1920; 

 Filatow, 1925a, 1934; Beckwith, 1927; Pasquini, 1927, 1932; von Ubisch, 1927; Gostejewa, 

 1935; etc. Mangold, 1931a, p. 263, gives in tabular form results obtained with different species 

 on lens formation by other than the presumptive lens epidermis. See also Stone and Dinnean, 

 1940, "Origin of the lens by induction in the salamander, Amblystoma piinctaUim,'" Proc. Soc. 

 Exp. Biol. Med., 40. 



