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THE AMERICAN NATURALIST [Vol. XLIl 



In the first place, a careful examination of serial sections 

 showed that nerves grow close to the region from which the 

 transplanted buds were removed. The finer twigs of host and 

 bud were thus brought into close union. It has been well es- 

 tablished by a number of investigators that the union of the 

 peripheral fiber of one nerve with the central fiber of another 

 permits the functioning or regeneration of the former. This 

 fact indeed is frequently taken advantage of in modern surgery. 

 Similarly accurate examination of serial sections showed con- 

 clusively that, in the transplanted limbs taken from "aneuro- 

 genic" individuals, nerves were present, and that these were 

 quite normal down to their minute details. There is thus pre- 

 sented the anomaly of a facial nerve, for example, growing along 

 entirely new paths, whose direction is determined by the struc- 

 tures in the limb. Such distribution is thus not a function of the 

 nerve, but of the organization of the limb which it innervates. 



These more accurate methods revealed the further fact that 

 accessory limbs, which are sometimes produced at the point of 

 transplantation, also contain nerves often in a high degree of 

 perfection. Braus had denied, on insufficient evidence, the pres- 

 ence of these nerves and had urged their absence as an argument 

 opposed to their centrifugal growth. 



By the aid of a very ingenious experiment, Harrison pushed 

 the inquiry one step farther. "Aneurogenic" individuals, 

 Braus and Harrison both found, were short lived. To over- 

 come this difficulty, Harrison grafted an "aneurogenic" tadpole 

 to the side of a normal or "nurse," and to the former he 

 transplanted a limb-bud from a normal individual. A develop- 

 ing nerve was thus transplanted to a nerveless region. Though 

 the results were not altogether satisfactory, the evidence pointed 

 to the conclusion that "there is no progressive development of 

 the nerve. On the contrary, there arc rapid regressive changes, 

 which in the majority of cases result in the entire disappearance 

 of the nerves within a few days after they are cut off from their 



On the whole, though the paper is exceedingly accurate — a 

 characteristic of Harrison's work — so far as it goes, it does not 

 settle the question, especially in the light of Bethe's recent con- 

 tribution. Perhaps, after all there is an element of truth on both 

 sides, and just how much value to put to each is the problem to 

 be decided. 



A. J. G. 



