242 PROCEEDINGS OF THE AMERICAN ACADEMY 



Paris, 1876) has drawn attention to the so-called Iridocystcs (Tnter- 

 fereiizellen of Briicke). They do not belong to the pigment, but 

 to optical colors, to fluorescence. A large number of small superposed 

 lamella! become luminous by contraction. They are very brilliant in 

 Saphirina and in a large number of fishes, allowing them to change 

 color according to the color of the bottom on which the lishes are 

 standing. They may occur in some insect larvte, but have not yet 

 been recorded. I believe that the arrangement in some insects' eyes 

 (Mantis), to be mentioned later, belongs to the Iridocystes. It should 

 be remembered that interference colors, one or both kinds, may occur 

 in the same place together with natural colors. The mirror spots 

 of Saturnia Pernyi show besides the interference colors a white 

 substance in the cells of the matrix, which Leydig believes to be 

 Guauin. But this fact is denied by Krukenberg for the same spe- 

 cies, and also for Attacus mylltta and Plasia chrysitis (vol. v. 1881, 

 p. 65). 



Natural Colors. 



There exist two different kinds of natural colors. 



1. The pigment is deposited in the form of very small nuclei in the 

 cells, or in the product of cells, in the cuticula. 



2. The pigment is a homogeneous fatty substance, a kind of dye 

 somewhat condensed. 



Pouchet speaks of a third kind of natural colors, which are said to 

 be inherent to certain tissues. He mentions them only for the muscles, 

 as I believe erroneously. So I have dropped entirely this kind of 

 colors till a more sufficient proof for their existence is given. 



The first kind of natural colors is to be compared with pigment 

 inclosed in air-tight glass tubes ; the second is related to a diffusive or 

 fluid pigment. 



The first kind of colors belongs to the cuticula, and I will call them 

 dermal colors. I consider them to be produced mostly by oxidation 

 or carbonization, in consequence of a chemical process originating and 

 accompanying the development and the transformation of insects. To 

 a certain extent the dermal colors may have been derived from hypo- 

 dermal colors, as the cuticula is secreted by the hypodermis, and the 

 colors may have been changed by oxidation and air-tight seclusion. 

 The cuticula is in certain cases entirely colorless, — so in the green 

 caterpillar of Sphinx oceUata ; but the intensely red and black spots 

 of the caterpillar of Papilio machaon belong to the cuticula, and 



