DSPARTMUNT OF EXPERIMENTAL EVOLUTION. 85 



Amblystoma tigrinum (larvae), Rana sylvatica (larvae) and other frog 

 larvae. 



These cave forms are in daylight : C(Bcidotea stygia, Biicrangonyx gracilis, 

 Cambarus pellucid us, Sinella cavernarum. 



RELATION BETWEEN THE HEREDITARY AND THE CHEMICAI, ACTION OP 



PIGMENTS. 



The studies of heredity of animal coloration quickly opened up questions 

 upon which it seemed probable light could be thrown only by chemical 

 studies. Accordingly a chemical laboratory was fitted up two years ago and 

 Dr. R. A. Gortner put in charge of it. The first problem which he attacked 

 was that of the melanins — their nature and behavior. To both these subjects 

 he has made substantial contributions. He reports as follows : 



The investigations as to the chemical nature of the animal pigments are as 

 yet in a very preliminary state owing to the unusual difficulties in purifying 

 these compounds. There appear to be two types of melanins, which are 

 differentiated by their solubility or insolubility in dilute acids. Those 

 melanins which are soluble in dilute acids are of a protein nature and do not 

 appear as granules under the microscope, but rather they appear to be a part 

 of the keratin structure and the coloration is diffuse as though the pigment 

 were dissolved in the keratin. Such a pigment is found in auburn Caucasian 

 hair. 



The granular pigments are, apparently, insoluble in dilute acids and the 

 nature of the molecule is still unknown. These melanins occur both alone 

 (in negro hair, brown Caucasian hair, some black feathers, etc.) and in com- 

 bination with the acid-soluble pigment or melano-protein (in black wool and 

 horse hair). 



In the study of these pigments there have been isolated 70 preparations, 

 which are divided as follows : 



No. of 

 preparations- 

 Black wool 35 



White wool 2 



Silky feathers 1 



Black Minorca feathers 3 



Black rabbit hair i 



White rabbit hair i 



No. of 

 preparations. 



Dominant white feathers 4 



Light brown horse hair 5 



Dark brown horse hair 5 



Brown Caucasian hair 6 



Auburn Caucasian hair i 



Other keratin structures 6 



A considerable number of these preparations have been analyzed more or 

 less completely, but much work is still necessary before the data can be 

 correlated. 



The formation of the animal pigments appears to be caused by an oxida- 

 tion induced by the presence of an oxidizing enzyme. The origin of the pig- 

 ment has been investigated in some of the insects : in the integuments of the 

 meal worm (Tenebrio molitor), in the cuticula of the periodical cicada 

 (Tibicen septendecim) , and in the elytra of the Colorado potato beetle 

 (Leptinotarsa decemlineata) ; the same general chemical reaction was found 



