350 sl-.M.MAKY OF CURRENT RESEARCHES RELATING TO 



blue rumps on black birds show granules much Larger than those in 

 other blue feathers. 



Pigment in silver feathers is distributed in the manner characteristic 

 for blue. In " silvers " the barbule surface appears greatly pitted and 

 roughened. The red and black pigments show pronounced differences 

 in their behaviour towards reagents and solvents. The intensity factor 

 has about the same quantitative value in blacks and reds, and results in 

 the formation, in intense birds, of about three times the amount of 

 pigment present in dilute birds. 



Passing to consider the genetic factors, the author holds that the 

 six fundamental self -colours of tumbler pigeons can be accounted for 

 by the interaction of four genetic factors: R, red: B, black; I. in- 

 tensity : and S, spreading. Evidence as to the nature of the factor B 

 has been secured from its effect on the feather pigment with respect to 

 («) colour, (b) manner of formation and distribution, (c) physical form, 

 and (d) chemical properties. All of these seem to indicate a different 

 mechanism from that which produces red pigment, rather than simply 

 a later stage of the same process. 



Uninfluenced by other factors, the final result of the pigmentation 

 process in a bird carrying B is the clumping of the pigment into the 

 middle of the barbule cells. The factor S, when present, stops this 

 clumping process and results in a " spread " condition of the pigment. 

 S may properly be considered as an inhibitive or " stopping factor." 



As regards the increment of pigment, the factor I has probably a 

 constant effect when acting on dilute birds of different constitutions, 

 namely, to increase by about three times the amount of pigment pro- 

 duced. As regards its influence on granule shape, on the other hand, 

 it reacts in a different manner with each combination of factors. The 

 facts concerning the granule shape in blacks suggest the possible exist- 

 ence of a factor not yet determined which is specifically concerned with 

 granule shape. 



The author remarks, in conclusion, that " genetic research which is 

 confined only to obvious characters is often superficial, and in such 

 cases microscopic research is necessary to distinguish the independently 

 heritable characters involved." 



Reactions of Amphibian Larva? to Light.* — Henry Laurens finds 

 that tadpoles of Rana pipiens and R. sylvatwa show no response to the 

 stimulus of light, while the larva? of Amblystoma punctatum are posi- 

 tively phototactic, both when normal and when deprived of their eyes. 

 The reactions of eyeless individuals are not brought about by the 

 stimulation of the central nervous system, but of the nerve endings in 

 the skin. Normal larva? placed in light become pale, blinded larvae 

 dark. Xormal larva? placed in darkness become dark, blinded larva? 

 pale. The condition of the pigment in the skin chromatophores does 

 not affect the sensitiveness of the .larva? to light ; but previous exposure 

 to light, or adaptation to darkness, does, in that dark -adapted larva? are 

 more sensitive to light than are those which have been kept in the light. 



* Journ, Exper. Zool., xvi. (1914) pp. 195-210 (2 figs.). 



