292 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
6. The same sort of reactions were obtained when only the eyes 
were exposed, as when the whole body was exposed, but there was a 
considerable decrease in the sensitiveness of the skin to differences in 
wave-lengths, compared with that of the eyes, or of the eyes and the 
skin. 
IV. Discussion. 
Sensitiveness to differences in wave-lengths is evidently a quality 
residing, not only in the eyes of the toad, but in the skin as well. It 
has been shown that the reactions when the skin alone was exposed 
to the lights were essentially the same as those when the eyes, or when 
the eyes and the skin, were exposed. It is necessary, therefore, to 
consider somewhat the nature of the photoreceptors in the eyes and 
in the skin. In the eye there is the retina, with its rod- and cone- 
cells, i. e., nerve-terminations differentiated for the reception of ether 
waves, which set up chemical changes in the rods and cones, and thus 
give rise to nerve impulses that are transmitted to the brain, and there 
perceived as light. In the skin are found the terminations of the spinal 
nerves. We are able to form some idea of how different lights appear 
to the toad when received through the eyes, but when we attempt 
to consider how they would appear when they are received through 
the skin alone, the problem becomes much more difficult. It has been 
found that in some amphibians there is a connection between the nerve 
terminations of the eyes and those of the skin, as is to be inferred from 
results when the skin is illuminated. Engelmann (’85) found that 
changes took place in the retinae of frogs when only the skin was 
exposed to light; though Fick (’90) obtained results which led him to 
conclude that interference with the normal respiration was the cause 
of these changes. Koranyi (’92) noted that illumination of the skin 
of the frog caused microscopic changes in the retina similar to those 
produced by the illumination of the eye itself. 
It is generally believed by modern physiologists that the perception 
of color is a function of the cones alone, and that the rods are sensitive 
only to light and darkness; and that, by virtue of their power of adap- 
tation in the dark, through the regeneration of visual purple, they 
form the special apparatus for vision in dim light. The generally 
accepted theories of color-vision all presuppose the existence of photo- 
chemical substances in the eye, which, when acted upon by the different 
wave-lengths of the visible spectrum, undergo different chemical 
changes, which give rise to different nerve-impulses that are trans- 
