80 The Mechanistic Conception of Life 



It has been known for some time that many animals, 

 especially certain fishes, adapt their color and pattern to the 

 ground upon which they happen to be. This fact has been 

 extensively utilized for the theory of natural selection. It 

 seems to me that the same facts furnish also the proof that an 

 image of the objects is formed in the brain. Pouchet many 

 years ago showed that the adaptation of fishes to the ground 

 ceases as soon as their eyes are removed or as soon as the forma- 

 tion of retinal images is prevented through the turbidity of the 

 refractive media of the eye. This fact (confirmed by many 

 observers) proves that the harmony between color and pattern 

 of the skin of fishes with their surroundings is transmitted 

 through the retinal image; in other words, that the so-called 

 adaptation of fishes to their surroundings is only the trans- 

 mission of the retinal image to the skin. 



It has, moreover, been shown that the destruction of the 

 optic fibers and the optic ganglia in the brain acts like the extir- 

 pation of the eyes; and finally it has been proved that the 

 cutting of the sympathetic fibers which go to the pigment cells 

 of the skin also prevents the formation of a picture of the 

 ground on the skin. Hence we know the path by which the 

 retinal image is transferred to the skin of fishes. One station 

 is the ending of the optic fibers in the brain. Since we are able 

 to prove the existence of an image of the object on the retina 

 of fishes; since it is proved that the image on the skin of the 

 fish is a picture of the retinal image but not of the object (in 

 this case the ground) itself; since, moreover, the transmission 

 of the retinal image upon the skin takes place through the 

 optic nerve, it follows that the image must pass the central 

 stations of the optic nerve during the transmission to the skin. 



An image consists of a number of points of different intensity 

 of light, the mutual arrangement of which is definite and char- 

 acteristic for the object. Sumner has shown that certain 

 fishes are able to reproduce on their skin rather complicated 



