406 ABSORPTION BY THE CHROMATROPE 



the blue) was absorbed to a very considerable degree by the living 

 cephalic pigment of the Mermis subnigrescens. The microscope field 

 was never completely and uniformly filled with the color of the 

 pigment. There were streaks at each margin of the field, and another 

 through the middle, that showed little color (see Fig. 1), so that 

 doubtless the absorption was not so pronounced as would be obtained 

 by dissolved pigment of equal density filling the entire field of the 

 microscope. 



A satisfactory demonstration was made by placing the object under 

 the microscope so as to produce absorption, and after the spectra had 

 been arranged for comparison, suddenly removing the pigmented 

 tissue. The effect produced by this instantaneous change was very 

 pronounced. The blue and violet region of the spectrum, hitherto 

 obscured by absorption, of course instantly assumed the same colors 

 as in the comparison spectrum. 



There seemed also to be some absorption in the outermost part of 

 the red of the visible spectrum, but, if so, it was very slight. No 

 absorption was noticed in the orange, yellow and green, and little if 

 any in the bluish green. 



The experiment was particularly satisfactory in that the pigment 

 was in a living condition. True, the head had been ligated and cut off 

 immediately before the spectroscopic examination, but from much 

 experience it is known that such a head continues to "live" and move 

 anywhere from a few hours to a day, or even more. 



Phototropes of somewhat the character here described probably 

 occur in the cervical region of many other nemas, particularly free- 

 living ones, the outer tissues of the neck serving as a cylindrical lens 

 for condensing light upon the pigmented tissues. Aquatic nemas so 

 situated as to utilize light rays penetrating water, not infrequently 

 present structures that may be suspected to be phototropes, now 

 that we have a clue to the nature of such structures in this phylum. 

 These primitive phototropes may well have been the forerunners of 

 the more highly developed phototropes, ocellate systems, of certain 

 nemas (e.g. Enchelidium). 



A general review of the nature and relationships of localized trans- 

 parent pigments in organisms in the light of the foregoing experiment, 

 may, perhaps, suggest new ideas and experiments with regard to their 

 functions both in animals and plants. 



