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Ross Granville Harrison 



cutting off from the dorsal edge of the body of the embryo at a 

 stage when the medullary folds had just closed, a thin strip con- 

 taining the spinal cord. At the time of this operation no visible 

 differentiation of fibers had taken place either within the central 

 nervous system or without, and the specimens passed through 

 their further development in the entire absence of peripheral nerves 

 except those derived from the head region, which had not been 

 injured. They lived and developed normally until theyolk absorp- 









n,sp(n- 

 coel 



Fig. I Cross section through the pronephric region of an embryo of Rana palustris 12 mm. long, in 

 which the absorption of the yolk is almost complete, a. ext., fore limb; vag., abdominal branch of the 

 r. lateralis vagi; n. spin., ramus abdominalisn. spinalis; coel., body cavity; c. br., branchial cavity. X 133. 



tion was complete or nearly so, a period varying with the tempera- 

 ture from seven to nine days.-^ At the end of this time the hind 

 limb buds were transplanted to normal larvae of the same age. 



-^Braus transplanted the nerveless limbs ten days after the removal of the spinal cord. The shorter 

 period of time represented in my experiments does not mean that the embryos had developed less than 

 those used by Braus but simply that they had probably developed at a higher temperature. It was 

 deemed unwise to keep them longer, for degenerative changes are very rapid after the yolk is absorbed, 

 and death soon follows. 



