258 PROCEEDINGS OP THE AMERICAN ACADEMY 



ever is found of them. The mimicry of the form and shape of other 

 insects is even more wonderful, but still unexplained, except as a pro- 

 tection. I have to confess, that just the unexplained mimicry of 

 form seems in some way opposed to my explanation of the mimicry 

 of colors. Science is in such questions still in its infancy, and the 

 first step is always the hardest. Every plausible suggestion is not 

 objectionable till a more convenient one has been given. 



As stated before, the dermal colors never change, the hypodermal 

 colors can change. Therefore mimicry of pattern is here excluded, 

 the hypodermal colors being the only ones on which the animal has 

 any influence, either involuntarily by the constant action of the nutri- 

 tive fluid, or voluntarily. 



If it could be proved by facts that by a kind of photographic pro- . 

 cess the colors of the surrounding objects can be transmitted, a great 

 step towards an understanding of mimicry in color would be attained. 

 The fact is probable, at least in some instances. I know no other 

 explanation, and the discovery that the seeing-purple in the eyes of 

 men and animals retains for a certain time after death the impression 

 of things and faces last seen, is in favor of my hypothesis. The eyes 

 of the insects contain a layer homologous to the seeing-purple, and 

 this layer is a decidedly hypodermal one. 



There is not much known about the color of the eyes of insects. 

 It may be said that perhaps all colors have been observed, from black 

 to white, brown, red, blue, green, golden, and in all different shades. 

 The color belongs to the chorioidea, and the pigment is included in 

 cells. Eyes without color pigment do not serve for vision. As the 

 colors are not persistent after death, they belong to the hypodermal 

 ones. Among Arthropods is to be found, just as in Vertebrates, the 

 peculiar organ called tapetum, a luminous colored spot on the under- 

 side of the chorioidea. The tapetum is recorded for Arachnida?, 

 Lepidoptera, and Diptera, and can cover the whole eye or parts of it, 

 or can form certain figures, as in Tabanidae and other Diptera. 



Leydig describes the tapetum of fishes as formed by small plates or 

 lamella? in very near juxtaposition. Only by a stronger pression the 

 iridescent lamellEe will become separated. Arthropods, for instance 

 Chrysopa, shows in the golden eyes small colored nuclei ; but in other 

 insects (Mantis) these nuclei alternate with iridescent plates. The 

 large Sphingidas and Noctuida? possess a peculiar tapetum. A verti- 

 cal cut through the eye shows underneath the dark pigment a silver- 

 white layer with a reddish front border formed by numerous and very 



