566 R- A. SPAETH 



These were illuminated during the actual period of observation 

 by means of a 16 c.p. electric light which had been found to 

 have no visible effect upon the melanophores. This was so 

 arranged as to preclude any possibility of its being a source of 

 error in the spectral illumination. 



In no case was a contraction of the melanophores observed 

 which could be unequivocally attributed to the action of the 

 monochromatic light. 



It seemed possible that the contraction observed in the earlier 

 experiments might have been due to ultra-violet light from the 

 arc-lamp. Through the courtesy of Mr. W. T. Bovie the ques- 

 tion of this possibility was definitely decided. 



The source^ of light for these experiments was a crystal-quartz 

 mercury- vapor lamp. This was placed below the stage of the 

 microscope and a copper jacket was slipped over the lamp-tube 

 with an opening so arranged as to fall immediately below the 

 center of the stage. At the side of this opening an ordinary 

 Ving-top' or 'fish-tail' burner tip was fastened. Through this 

 a blast of air was blown throughout the experiments. This 

 prevented any possible heat effects. As an additional precau- 

 tion a thermometer lay within the illuminated field in which the 

 temperature never rose above 23°C. 



After the melanophores had been completely expanded in a 

 0.1 M. NaCl solution in the usual way the scales were exposed 

 to the ultra-violet rays in a cell, the bottom of .which consisted 

 of a piece of crystal quartz 1 mm. in thickness, and 4 cm. from 

 the lamp. Repeated exposures of scales placed face up in the 

 solution, that is, with the bony plate of the scale interposed be- 

 tween the source of light and the melanophores, gave no reac- 

 tion. When, however, the scales were inverted, that is, turned 

 with the melanophores towards the light, in this case the quartz 

 bottom of the cell and the thin epidermis being the only possible 

 sources of interference, a very definite reaction followed. 



' This lamp was made by Mr. Bovie of Heraeus crystal quartz tubing 8 mm. in 

 diameter with walls 1 mm. thick. The arc was 10 cm. long and the amperage 1.25. 

 The wave-lengths were in the region 185-290 /x/i. 



