48 



SCIENCE 



[N. S. Vol. XLIX. No. 1254 



observed iu the laboratory, and occurring in 

 a similar way in nature. 



The Importance of Nivation as an Erosive 

 Factor, and of Soil Flow as a Transporting 

 Agency, in Northern Greenland: W. Elmer 

 Ekblaw, Crocker Land Expedition, American 

 Museum of Natural History, and University 

 of Illinois. ISTivation and solifluction, char- 

 acteristic processes of disintegration and de- 

 nudation under subarctic or arctic conditions, 

 appear to be of prime importance in the re- 

 duction of high relief of northern Greenland. 



On the a-Holomorphisms of a Group: G. A. 

 Miller, Department of Mathematics, Univer- 

 sity of Illinois. A solution of the problem : 

 Eor what values of a is it possible to con- 

 struct non-abelian groups which admit sep- 

 arately an a-holomorphism ? 



The tenth number of Volume 4 contains 

 the following articles : 



Measuring the Mental Strength of an Army: 

 Major Eobert M. Yerkes, Sanitary Corps, N. 

 A. A review of the psychological undertak- 

 ings in connection with the examination of 

 the recruits for the U. S. Army. 



Thermo-Electric Action with Thermal Effu- 

 sion in Metals: A Correction: Edwin H. Hall, 

 Jefferson Physical Laboratory, Harvard Uni- 

 versity. Supplementary to an earlier paper. 



Invariants and Canonical Forms: E. J. Wil- 

 ezynski. Department of Mathematics, Univer- 

 sity of Chicago. A general proof in the sense 

 of Moore's general analysis of the fact that 

 the coefficients of a unique canonical form are 

 invariants. 



Types of Phosphorescence: Edward L. Nich- 

 ols and H. L. Howes, Department of Physics, 

 Cornell University. Two types of phosphor- 

 escence known as persistent, and as vanishing, 

 are distinguished and discussed. The types 

 are apparently independent, and both may oc- 

 cur with a single source of excitation, and in 

 a single substance. 



The Smithsonian " Solar Constant " Ex- 

 pedition to Calama, Chile: C. G. Abbot, Smith- 

 sonian Astrophysical Observatory. A prelim- 

 inary report on the aim and equipment of the 

 Calama Expedition. 



Maroon — A Recurrent Mutation in Droso- 

 phila: Calvin B. Bridges, Marine Biological 

 Laboratory, Woods Hole. 



Edwin Bidwell Wilson 

 Massachusetts Institute or Technology, 

 Cambridge, Mass. 



SPECIAL ARTICLES 



ON THE NATURE OF THE PIGMENTATION 



CHANGES FOLLOWING HYPOPHYSECTOMY 



IN THE FROG LARVA 



It has been shown by Smith^ and by Allen^ 

 that the removal of the hypophysis fundament 

 from the young larval frog is followed by a 

 marked change in pigmentation. Within seven 

 to ten days after the operation — which is most 

 successfully performed when the larva is 3.5— 

 4.0 mm. in length — the color of the tadpole 

 changes from black to " silvery," or as Smith 

 describes it, the larva becomes an albino. 



Smith and Allen hold quite different views 

 as to the nature of this pigmentation change. 

 Smith thinks that the silvery appearance of 

 the operated tadpoles is due to a reduction in 

 the number of melanophores in the epidermis 

 and to a loss of the individual pigment gran- 

 ules contained in these melanophores. He 

 states that the melanophores are equally ex- 

 panded in the albinos and in the controls, 

 " consequently the lighter color of the albinos 

 can not be due to the contracted condition of 

 the chromatophores but must be referred, in 

 part, to the reduced number of melanin gran- 

 ules in the pigment cells of the epidermis." 



Allen, on the other hand, believes that the 

 lighter color of the operated larvse is due to 

 the fact that the epidermal pigment cells have 

 migrated to deeper positions and that the 

 pigment cells are contracted throughout all 

 parts of the body. He is convinced that 

 " there is no disappearance and bleaching of 

 pigment granules as asserted by Smith." Each 

 of these observers, apparently, has based his 

 conclusions upon the study of sections en- 

 tirely. It will be recognized readily that in 



1 Smith, P. E., Anatomical Beeord, Vol. 11, p. 

 57, 1916. 



2 Allen, B. M., Biological Bulletin, Vol. 32, p. 

 117, 1917. 



