DEPARTMENT OF EXPERIMENTAL EVOLUTION. 83 



Some time has been devoted by Dr. Banta to a comparative study of the 

 light reactions of the cave form of the amphipod Eucrangonyx gracilis and 

 the form of the same species found in surface streams in the same localities. 

 The work on the normal light reactions of these forms should be completed 

 soon. Two parts of a similar study, "A comparison of the reactions of a 

 species of surface isopod with those of a subterranean species," previously 

 completed, have been published during the year in the Journal of Experi- 

 mental Zoology. With the species used, Asellus communis and its near rela- 

 tive of cave habitat, Ccecidotea stygia, there was found a great difference in 

 reactiveness to light and to mechanical stimulation. The cave form was re- 

 sponsive (negatively) only to rather high intensities of light, while it was 

 exceedingly responsive to all sorts of mechanical stimulation. On the other 

 hand, Asellus was responsive (also negatively) to comparatively low light 

 intensities, though it fell far behind Ccecidotea in its responsiveness to tactile 

 stimulation. With Ccecidotea there was increased sensitiveness to one sort 

 of stimulation to compensate for partial loss of responsiveness to another 

 sort. Having a bearing on the respective habitats of the two species was the 

 fact that Asellus is positive in its response to light after retention in darkness 

 for a time, while Ccecidotea is always negative to any intensity to which it 

 responds at all. Hence Asellus, if happening within a cave, would tend to 

 leave it after a time if, by chance, it came within reach of the light from out- 

 side, while Ccecidotea is always negative in its response and responds to a 

 sufficient range of intensities to prevent its leaving a cave and passing into 

 daylight outside. 



Studies have been made on sex recognition and the breeding-habits of 

 Asellus. An unsuccessful attempt was made to breed from an albino strain 

 of Asellus, but the experiment is being continued. 



Observations are being made for possible modifications in light reactions 

 as well as pigment changes in the various forms in their changed environ- 

 ments ; and upon the effect of absence of light upon the development of cer- 

 tain amphibian larvae. 



CHEMISTRY OP PIGMENTS. 



During the past year Dr. R. A. Gortner has been in charge of the chemical 

 laboratory fitted up for his use, in the study of organic pigmentation. He 

 reports as follows : 



During the past year the investigations carried out in the chemical labora- 

 tory have been largely of a preliminary nature. In pursuance of an endeavor 

 to ascertain the origin, mode of formation, and chemical nature of com- 

 pounds of the melanin class it was found necessary to determine the form in 

 which the pigment is present in the animal body, skin, hair, or feathers. The 

 greater part of the time has, therefore, been utilized in isolating the pigment 

 from black sheep's wool by destroying the keratin structure with alkali or 

 acid of varying concentration, then purifying the melanin and subjecting it 

 to a chemical analysis. By a comparison of the data from this series the 

 effect of alkali or acid upon the melanin molecule could be determined. 



