No. 518] 



REGENERATION 



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tion the case of Lumbriculus. The histogenesis of the 

 regenerated organs in this worm was studied very ex- 

 tensively by at least four investigators. There is 

 scarcely a point of any importance upon which all are 

 unanimously agreed. Unless one shares Davydoff's 

 rosy optimism that " whatever is last is best/' and that 

 the latest contribution to the subject is necessarily the 

 truest, the non-committal attitude of skepticism would 

 seem far preferable. 



Furthermore, the histological studies of the regenera- 

 tive process have likewise revealed certain striking devi- 

 ations from the usual course of things. Wolff's re- 

 searches of the regeneration of the lens in salamanders 

 showed that in regeneration the lens is formed by a 

 method entirely different from that observed in embry- 

 onic development. In the embryo it arises as a thicken- 

 ing of the ectoderm covering the optic cup, while in re- 

 generation— "Der Obere Irisrand ist namlich offenbar 

 die zweckmassigste stelle fur die Enstehung der Linse." 



Hazen discovered that in the anemone Sagartia the re- 

 generation of the oesophagus involved some important 

 departures from the ontogenetic process. 



In small pieces the oesophagus regenerates as an invagination of 

 mesoglaea and endoderm in the shape of an inverted cup, in which the 

 mesoglaja forms the middle layer, and whieh is covered on both outside 

 and inside by entoderm. The ectoderm takes no part in the regenera- 

 tion of the (esophagus. 



Margaret Eeed found that the muscles of a regener- 

 ating appendage in Crustacea originate entirely from 

 ectodermal cells. "When the first leg of the crayfish is 

 thrown off at the breaking joint, no muscles are injured, 

 and the muscles for the new leg are formed from cells 

 proliferated by the ectoderm. In the hermit crab also 

 the muscles of the new leg are formed by ectodermal 

 cells." In ontogeny the muscles originate from endo- 

 derm. 



The last discovery is of particular importance, not 

 only on account of the different methods of muscle-for- 



