358 OSCAR RIDDLE. 



tophores " which contain a pigment. At the points of resistance 

 chiefly the muscles of the body wall — the pigment is piled up 

 and contributes strikingly to the color pattern. 



The earlier work of Eisig 1 on the coloration of the Capitel- 

 lidse presents certain analogies to the work just mentioned. This 

 investigator states that in these forms certain color areas arise 

 through the transformation of blood-disc clusters which lie between 

 the cuticle and hypodermis ; the transformation being due to 

 stagnation of the blood flow after invasion by excretory (pigment) 

 particles. Each of the two works just cited undoubtedly throws 

 much light on the coloration of the forms studied ; but it may 

 also be remarked that the origin of the pigment in both cases is 

 still somewhat in question, and that the results do not seem to 

 be of wide application. In fact, it is now evident- that no theory 

 which considers pigments as waste products, tossed about by the 

 circulation until they find some sort of excretion, can be of general 

 application. 



Certain pigmentary colors in the color-patterns of several orders 

 of insects have been pointed out from time to time by various 

 workers as being correlated with certain structures — spiracular 

 openings, venation, attachments of muscles in the body wall, 

 positions of other internal organs, etc. In all these cases, how- 

 ever, little more than " correlation " has been accomplished. We 

 have yet, I believe, to obtain anything approaching a complete 

 and unequivocal explanation of any of these associations. 



The facts observed by Loeb on the chromatophores in the 

 yolk-sac and embryos of Fundulus are perhaps the most helpful 

 of the few similar studies thus far made on vertebrates. The 

 observation of an actual and definite migration of entire chroma- 

 tophores (of two types) into a definite color pattern, and this under 

 some (?) influence exerted by the circulating blood forms two im- 

 portant steps toward a physiological explanation of the colora- 

 tion in question. It should not be overlooked, however, that the 

 final step would involve a much better knowledge of the nature 

 of the influence which the blood brings to bear on the chromato- 

 phores ; and further it may be said that in the explanation of the 

 color- patterns of animals it seems at present that this mechanism, 

 too, has a rather restricted application. 



1 Eisig, H., "Die Capitelliden," Naples, Monograph, 1887. 



