PROBLEMS OF ORGANIZATION 211 



to be analyzed is shown in Rose's ('44) study of anuran forms, where 

 the cuticle forms a block to the regenerative process. By treating with 

 NaCl the stumps of amputated limbs in fully developed frogs or in frog 

 tadpoles after the normal time of regeneration, Rose was able to initiate 

 limb development which was sometimes complete, and at other times 

 with deficiencies in the hand. 



Singer ('42, '43, '46a, '46b, '47a, and '47b) has analyzed the amount 

 of nerve tissue necessarily present in order to initiate regeneration. He 

 finds that the process is non-specific and that the number of nerve fibers, 

 whether autonomic, sensory, or motor, controls the reaction. In this way 

 the regenerative process of urodeles is reduced to a quantitative expres- 

 sion of nerve fiber relationship and our concept of the significance of 

 nerves to regeneration is clarified. 



In the above pages a few of the problems of organization have been 

 presented. They constitute but a sample of the vast array which have at 

 one time or another been investigated and for which at present there is 

 no final answer. The work here given, however, shows the present attack 

 on problems many of which were formulated long ago. It must be ad- 

 mitted that their final solution has not been attained, but we have reason 

 for optimism, for science works slowly but surely toward the solution 

 of any major problem, such as embryonic organization has proved to be. 



REFERENCES 



Baltzer, F. Uber erbliche letale Entwicklung und Austauschbarkeit artver- 

 schiedener Kerne bei Bastarden. Naturiviss, 28, 177-187, 1940. 



Barth, L. G. Neural differentiation without organizer. /. Exp. Zool., 8y, 

 371-383, 1941. 



Boell, E. J. Biochemical and physiological analysis of organizer action. 

 Growth, Vol. 7 (Suppl.), 37-53, 1942. 



Boell, E. J. Functional differentiation in embryonic development. II. Respi- 

 ration and cytochrome oxidase activity in Amblystoma punctatum. 

 /. Exp. Zool, IQO, 331-352, 1945. 



Boell, E. J., and S. C. Shen. Functional differentiation in embryonic devel- 

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Boveri, Th. Zellenstudien VI. Die Entwicklung dispermer Seeigeleier. Ein 

 Beitrag zur Befruchtungslehre und zur Theorie des Kerns. Jen. Zeit- 

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Boycott, A. E., and C. Diver. On the inheritance of sinistrality in Limnaea 

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