NEW EXPERIMENTS ON LIGHT REACTIONS 7 



and herewith it is proved that the beautiful blue on breast and 

 tail of this bird cannot be for adornment. 



Among the night birds I found the motor values like those of 

 the color blind human eye, a fact which corresponds to the 

 superior number of rods and cones in the retina of these birds. 

 The relatively slight differences are sufficiently explained by the 

 fact that in the retina of the night birds, the cones are not en- 

 tirely lacking as many assume; indeed, I have repeatedly been 

 able to count in such retinas one to two million cones, with 

 slightly colored oil balls. 



Among the invertebrates, examination with the new appa- 

 ratus of the movements of the pupils of Cephalopods, which are 

 particularly well suited to the measuring experiments, shows as 

 you see striking conformity to the irritative values for the totally 

 color-blind human eye. By the use of other methods also, I 

 have been able to show that these invertebrates are totally 

 color-blind. I cannot here dwell on these new experiments. 



A glance at the table will show you further that the motor- 

 sensitiveness of bees to colored lights, of mollusks (Psammobia) 

 and of sea urchins (Centrostephanus) is almost identical with 

 that of a color-blind man, whereas it differs characteristically 

 from that of red-blind eyes. The reaction of bees I need not 

 mention again, as the bees as well as fish and crabs may easily 

 be proved totally color-blind by other methods which I have 

 developed. The continually repeated mistaken assertions of a 

 few zoologists, from which a color sense in these animals is sup- 

 posed to be deducible, need no new refutation after the above 

 measurements are studied by anyone at all familiar with the 

 subject. 



The advantages of the new methods of research which I have 

 here briefly indicated consist essentially in the following points: 

 All the light reactions which I have hitherto carefully investi- 

 gated in animals, the contraction of the pupils in birds and in- 

 vertebrates, the swimming of fish and crabs and the flying of 

 bees toward the light, the phenomena of retraction in Serpula 

 and Psammobia, the rotations of the little clubs in the Centro- 

 stephanus, etc., all these manifold movements which are caused 

 by increasing or lessening the light, we are able by the help of 

 our apparatus to measure with the identical, physically exactly 

 determined colored lights, and to express their motor-sensitive 



