286 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are expanded, those of the eyeless larvae contracted. The melanophores 

 of normal larvae kept in bright diffuse daylight on a white background 

 are contracted ; on a black background, expanded. 



On the other hand, the primary reactions of the melanophores of 

 normal and eyeless larvae are identical, light bringing about an expan- 

 sion, darkness a contraction. The response of the eyeless larvae is much 

 slower. After some time the condition undergoes a secondary change, 

 as above indicated. 



The melanophores of blindfolded larvae, when illuminated, act like 

 those of eyeless larvae — they expand and remain so. In darkness they 

 act like those of normal seeing larvae — at first they contract, but after 

 five days or more they expand. The reactions of recently metamorphosed 

 young adults are like tiiose of adults, but slower and less complete. 

 The melanophores of very young larvge do not react to light, darkness 

 or backgrounds. 



The melanophores in isolated pieces of skin, suspended in drops, do 

 not react to daylight, to light from a Nernst glower, or to darkness. 

 They contract in the light of an arc-lamp, probably responding to the 

 ultra-violet rays. A O'Ol p.c. solution of chloretone inhibits this effect. 

 Solutions of NaOl, KCl, and atropin have no effect. Atropin sulphate 

 (1 p.c.) and curare (0*2 p.c. and 0"1 p.c.) cause expansion in larvge, not 

 in isolated pieces of skin. Chloretone produces expansion, and inhibits 

 the effects of light and darkness. In a " Ringer solution opacum " 

 larvffi will live for twenty days, and the melanophores will respond 

 normally. 



Low temperature causes expansion, high temperature (above 28° C.) 

 contraction. The melanophores are under both spinal and sympathetic 

 nerve control, the former being relatively unimportant. The sympa- 

 thetic fibres leave the spinal cord by means of the first or second, 

 possibly both, spinal nerves. When the portion of the central nervous 

 system in front of this is destroyed, the secondary reactions no longer 

 take place, though the primary reactions are normal. The latter are due 

 essentially to direct stimulation, helped by stimulation through the eyes. 

 The secondary reactions of normal seeing larvae are due to nervous 

 activities, set up by stimulation of the retina?, but in which supposed 

 sensory endings in the skin have little or no share. The indirect stimu- 

 lation at first assists the direct. In a " 2 p.c. solution of curare the 

 larvfB soon become immobile, and the pigment-cells remain expanded 

 under all conditions. If a small amount of 1 p.c. solution of curare 

 be injected into the body-cavity, the larva are rendered immobile, but 

 the melanophores react as usual. If a drop or two of 1 p.c. solution of 

 strychnine be injected, the melanophores soon contract after the cramp 

 begins, which points to a spinal control. If a few drops of O'Ol p.c. 

 of nicotine be injected, the primary reactions take place as usual. An 

 induced current of sufficient strength and duration causes the melano- 

 phores to contract in normal larva, in larvte in which the central nervous 

 system has been destroyed, in excised portions of the body, and in 

 isolated pieces of skin. A constant current causes the melanophores to 

 expand. Light, temperature, and electric currents all act directly on 

 the melanophores. Light and electric currents act also indirectly on 



